US 2897067 A
Description (OCR text may contain errors)
2,897,067 Patented July 28, 1959 ALCOHOL-CON TAININ G GASOLINE COIVIPOSI'HON William J. Sparks and David w. Young, Westfield, N..l., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application November 26, 1954 Serial No. 471,492
2 Claims. (Cl. 44-56) This invention relates to naphtha base gasoline fuel compositions of balanced volatility containing substantial amounts of butanes and isopropyl alcohol.
It has been known for some time that isopropyl alcohol contributes valuable properties to motor gasoline, particularly in terms of anti-stalling properties and high octane number. However, it has also been known that the alcohol tends to increase the front-end volatility and especially the so-called Reid vapor pressure of the resulting blend. Consequently the addition of alcohol is made at the expense of limiting the permissible butanes content of the gasoline if standard vapor pressure specifications are to be met. Stated differently, a small amount of isopropyl alcohol sharply increases the vapor-to-liquid ratio of a gasoline composition and tends to cause vapor lock problems unless the customary amount of butanes is correspondingly reduced. See US. Patent 2,579,692, column 9, lines 9-37. Since butanes normally constitute one of the least expensive ingredients of a motor fuel, their replacement by isopropyl alcohol has not been deemed economically attractive except at very low concentrations such as l to 2.5 percent. At the same time fuels containing large concentrations of alcohols have been known to have limited potentialities because, on a Weight basis, their heat of combustion is considerably less than the heat of combustion of hydrocarbon gasoline fractions. Consequently, gasolines containing comparatively large amounts of alcohols have not seemed to possess much interest for use in modern, high-compression engines of high intended'power output.
It is among the objects of this invention to produce an economical, high-octane motor fuel making the maximum use of butanes and butenes. Another object is to improve the octane rating of hydrocarbon gasoline base stocks with the aid of alcohol, without upsetting their volatility distribution. Still another object is to improve the octane rating of such base stocks without primary reliance on severe naphtha reforming. These and other objects, as Well as the nature and scope of this invention, Will become more clearly apparent from the subsequent description.
It has now been discovered that as the isopropyl alcohol content of a gasoline motor fuel is gradually increased beyond the conventional low value, a point is reached where the further addition of the alcohol brings about an unexpected net decrease in Reid vapor pressure of the resulting blend. Thus, more specifically, the surprising fact was discovered that while the addition of less than about 4 percent of isopropyl alcohol tends to increase the volatility of a gasoline more or less considerably, the addition of 4 to. percent and especially of about 6 to. 8 percent of the alcohol increases the original volatility of a gasoline hydrocarbonbase relatively little, mostly in the middle-volatility range at around 200 F., and actually tends to decrease the front-end volatility quite appreciably.
As a result of this discovery it has been found that superior motor fuels can be formulated containing substantial amounts of isopropyl alcohol without requiring the backing out of butanes to less economical uses; and the increased middle volatility contributes to improved Warm-up characteristics. At the same time it has been found that as long as the isopropyl alcohol content of the gasoline is kept below about 8 or 10 percent, no significant reduction of available power or motor performance is observed. This is due to the fact that the moderate decrease in heat value is effectively compensated, and frequently more than compensated, by a corresponding improvement in anti-knock properties attributable to the alcohol. The relatively high latent heat of the alcohol also has been found to improve the specific output of engines in that it tends to reduce the intake manifold temperatures and consequently increasesthe quantity of charge in the cylinder. Only when the alcohol content is raised substantially beyond the 10 percent level does the motor performance begin to suffer from the reduced calorific value'of the fuel. Higher concentrations of isopropyl alcohol have also been found impractical because, on contact with water in storage or the like, they tend to result in an objectionable separation of the blended fuel mixture into two phases.
Thus the present invention relates to the economic as well as quality upgrading of gasoline hydrocarbon base stocks of relatively high volatility. In other words, the invention is applicable to hydrocarbon gasoline base stock containing substantial amounts of C and C bydrocarbons and accordingly having a Reid vapor pressure between about 7 and 14 p.s.i. More specifically the invention applies to gasoline base stocks having a gravity of about 55 to 60 API, containing about 4 to 20 percent butanes and butenes, and having an A.S.T.M. distillation such that about 15 to 30 volume percent of the gasoline stock, counting recondensed distillate as well as uncondensed distillation loss,'is evaporated below 158 F., about 55 to 70 percent is evaporated below 257 F and about to percent is evaporated below 356 F. It will be recalled that the 158 F. point is usually taken as a measure of front-end volatility or start-up and vapor lock characteristics Whereas the 257 F. point is usually taken as a measure of intermediate volatility or performance of the fuel during engine warm-up; the 356 F. point gives an indication of the proportion of high boiling constituents and is taken as an indication of proper distribution and absence of excessive lubricant dilution to be expected from the fuel. The initial boiling point of the hydrocarbon base stock is between about 85 and F., and the final boiling point at about 320 to 430 F., exclusive of any solvent oil which may also be present. For high anti-knock motor fuels, the research octane number of the hydrocarbon base stock should preferably be in excess of 80, and its net heat of combustion from about 116,000 to 130,000 B.t.u./gal
lon, depending on gravity and other considerations.
The hydrocarbon base stock normally is a blend of a variety of individual stocks, notably butanes or more properly a C cut including both butanes and butenes; pentanes or a 0 C out including both paraifins and olefins; light virgin naphtha; depentanized and undercut catalytic naphtha; depentanized and undercut reformed naphtha; depentanized 400 F. end-point reformed naphtha; depentanized 400 F. end-point. thermally cracked naphtha from gas oil and reduced crude; catalytically cracked heavy naphtha boiling between about 300 and 420 F.; thermally cracked heavy naphtha; hydroformed naphtha; alkylate' obtained by combining'a C -C olefin with an isoparaflin such as isobutane; and
polymer gasoline obtained by thermal or catalytic 'polyv merization of propylene, butenes and pentenes and mixtures thereof.
The blending of these components to meet the aforementioned specifications is a well-known art. Thus butanes are used to control Reid vapor pressure, pentanes and light virgin naphtha to control front-end volatility, while the volatility and octane level of the total available gasoline pool is usually controlled by the severity of the reforming operation so as to produce a balanced pool meeting the aforementioned specifications.
The specifications of course varywith the seasons. For instance, summer grade gasoline's' may normally have a Reid vapor pressure of about 7 to 10 psi. and a C, content of about 4 to 8 percent; spring grade gasolines a vapor pressure of about 11 to 12 p.s.i. and about 9 to 12 percent C hydrocarbons; and winter grade gasolines a vapor pressure of about 13 to 15 p.s.i. and about 13 to 18 percent 0,, hydrocarbons. While the invention is applicable to all of these formulations, it is particularly valuable, and its efi'ect is particularly unexpected, in con nection with the more valatile, winter-grade type gasolines.
In addition to the hydrocarbon gasoline base, the other main ingredient of the novel fuel compositions is isopropyl alcohol. This alcohol may be used either in a high state of purity, e.g. at least 98% pure, or it may be a mixture such as that obtained by direct hydration of propylene over' tungsten oxide. Such a mixture will normally contain a major proportion, e.g. 55 to 95 percent, of the alcohol and minor amounts of other organic compounds such as isopropyl ether, acetone, liquid propylene polymer, etc. The water content of the alcohol is preferably not in excess of about 0.5 percent, so as to avoid undesirable phase separation and resulting loss of alcohol from the motor fuel blend. As stated' earlier, the amount of isopropyl alcohol used in accordance with the present invention may range from about 4 to 10 parts,
Table II I EFFECT OF ISOPROPYL ALCOHOL ON GASOLINE VOLATILITY IPA, percent Reid Change I. .P., 10% off 20% ofi 40% off in blend V.P., in RVP, F. at F. at F. at F.
It is apparent from the data that the addition of up to about 3 percent of alcohol lowers the initial boiling point, raises the Reid vapor pressure, greatly increases the amount distilling at 122 F., 140 F. and 149 F., and hence increases the tendency for vapor lock. Thus, when such low concentrations of alcohol are blended into a hydrocarbon base stock, the latter must have a considerably 7 reduced butanes content as compared with a similar alcohol-free gasoline of the same Reid vapor pressure. This amount of backed-out .butanes may equal to about 1 to 5 percent based on the gasoline, as compared to otherwise tolerable amount, if the Reid vapor pressure of the blend is to stay between about 7 and 14 lbs. Such displacement of cheap butanes naturally represents 'a or preferably between 6 and 8 parts per 100 parts of hydrocarbon base. It will be understood that, in the absence of contrary indications,all percentages and ratios of liquid ingredients are stated on a volume basis throughout this specification and appended claims' The operation and advantages of the present invention will be further illustrated by specific examples.
EXAMPLE 1 The effect of varying amounts of essentially anhydrous pure isopropyl alcohol on the volatility of a regular grade gasoline base stock is summarized in Tables I and II. Table I shows the effect of alcohol concentration on the Engler distillation curve of the blend in terms of amounts distilling at specified temperatures. Table II is based on the same data but correlates the alcohol concentration with the temperatures at which specified percentages of the blend distill over; and also shows the Reid vapor pressure of the blends. For the sake of convenience, isopropyl alcohol is abbreviated as IPA in the tables.
Table I EFFECT OF ISOPROPYL ALCOH OL 0N GASOLINE VOLATILITY r Percent distilled at temperature indicated IPA, percent Initial in blend B.P.,
91 6. 5 12. 5 15. O 18. 0 21. O 40. O 80. 0 89. 5 8. 5 15. 0 18. 0 20. 5 23. 5 41. O 80. 5 93 8. 0 16. 0 20. 0 23. 5 26. 5 43. 5 81. 5 94 6. O 14. 0 19. O 24. 0 28. 5 44. 0 80. 5 95 7. U 15. 0 20. 0 26. 0 32. O 46. 5 81. 5 97 5. 0 13. 5 18. 5 25. 0 33. O 48. O 81. 5 94 5. 0 l3. 0 18. 0 25. 0 35. 0 50. 5 82. D 100 5. 0 13. 5 18. 5 25. 5 39. O 55. 0 84. 0
major economic consideration.
In contrast the addition of 4 to 15% of alcohol causes a progressive rise in initial boiling point, a progressive decrease in the amount distilling at 122 F., F. and 149 F., and a corresponding drop in Reid vapor pressure. When the alcohol is present in amounts in excess of about 5%, the Reid vapor pressure as' well as the amounts distilling at 122 F. are actually lower than in the case of the alcohol-free stock. Consequently, with 4% or more of alcohol such a gasoline may actually contain'increased amounts of inexpensive butanes without exceeding front-end volatility specifications.
Another point to bear in mind is that while increasing the amount of alcohol in excess of 4% decreases the front-end volatility of the hydrocarbon stock, the amount distilling at 15 8 F. becomes substantially constant at about 8% alcohol, indicating that this much alcohol is suflicient to satisfy the azeotrope which the alcohol forms with the lower-boiling hydrocarbons and which boils at about 158 F. On the other hand, increasing the amount of alcohol in excess of 8%, and particularly in excess of 10%, results in an ever increasing rise in middle volatility as indicated, for instance, by the amount distilling at 212 F. Thus, an increase in alcohol content from 4 to 8% increases the amount distilling at 212 F. from 43.5 to 46.5%, or to a value only about 15% higher than in the case of the alcohol-free stock. But when the alcohol content of the blend is increased from 10 to 15 the amount distilling at 212 F. jumps from 48 to 55%, or to a value almost 40% higher than in the case of the alcohol-free stock. On still another basis it can be seen that whereas in the 4 to 8% alcohol range the intermediate volatility of the blend at 212 F. is increased about 0.75 point for each percent of alcohol added, in the 10 to 15% alcohol range the intermediate volatility in-' creases at almost twice that rate, i.e., at 1.4 points for each percent of alcohol added. Such high increases in middle volatility may of course be undesirable because of loss in heat content.
The data in Table II are interesting, and particularly striking when plotted to show the change in Reid vapor pressure due to the addition of various amounts of isopropyl alcohol. They show especially clearly the critical nature of the 4% alcohol concentration limit andalso the excessive efiect of alcohol concentrations greater than about 8 or 10%. Specifically, it can be seen that increasing the isopropyl alcohol concentration from 0 to distills.
about 3% greatly increases the Reid vapor pressure and reduces the temperature at which a given proportion of the lower boiling fraction distills. This increases the likelihood of bothersome vapor lock, unless otherwise compensated for. In contrast, further increases in alcohol content above 4% progressively reduce the critical front-end volatility as indicated by a decrease in Reid vapor pressure, an increase in initial boiling point, as well as the temperature at which 10% and 20% of the blend The middle volatility as measured by the temperatures at which 40% or more of the blend distills is progressively increased as more and more alcohol is added. It will be noted that this increase in middle volatility is comparatively mild at concentrations of less than 10% alcohol, and actually results in improved warm-up characteristics. However, the eifect of the alcohol on middle volatility becomes quite abrupt at the higher concentrations and may result in an excessive loss in heat content as mentioned earlier. Specifically, where 10% alcohol reduces the cut-ofi' point of the 40% fraction by about 24 F. as compared with the alcohol-free gasoline, a further 5% alcohol increase reduces the cutoff point of the 40% fraction almost another 20 F. to a temperature which very nearly corresponds to the 20% cut-off point of the alcohol-free blend. In other WOIdS, the volume of the l5%-alcoh0l blend distilling at 170 F. is almost twice as large as the volume of the alcoholfree blend distilling at the same temperature.
EXAMPLE 2 The practical value of the present invention is further illustrated by the data summarized in Table III. This table shows the Reid .vapor pressure (RVP) of various three-component blends made up from (a) isopropyl alcohol (98% pure), (b) normal butane, and (c) a debutanized naphtha stock having a Reid vapor pressure of 5.5 p.s.i.g., using concentrations of 0, 2, 6 and 10% alcohol on the final blend. It will be observed that these various blends have been made up to meet five different specifications relative to vapor pressure, types 1 and 2 being representative of summer grade gasoline, type 3 being representative of spring grade gasoline, and types 4 and 5 being representative of winter grade gasoline.
Table III EFFECT OF ALCOHOL ON BUTANE TOLERANCE Blend type 1 2 3 5 5 RVP of blend, p.s.i.g 7.6 9.4 11.1 13.2 14.4
Blend number- 1a 2a 3a 4a 5a Blend composition, percent:
0 0 0 0 4. 0 7.0 10.0 14. 0 16.0 Base 96. 0 93. 0 90. 0 86. 0 84. 0 Gals. butane/100 gals. base 4. 2 7. 11. 1 16. 3 19. 0 Blend number 1b 2b 3b 4b 5b Blend composition, per
Alcohol 2. 0 2. 0 2. 0 2. 0 2. 0 3. 2 6. 3 9. 2 13.0 15.0 Base 94. 8 91. 7 88. 8 85. 0 83. 0 Gals. butane/100 gals. base-- 3. 4 6. 9 10.4 15. 3 l8. 0 Blend number 1c 20 3c 40 5c Blend composition, percent:
Alcohol 6. 0 6. 0 6. 0 6. 0 6.0 Butane 3. 8 6. 6 9. 4 13. 2 15.0 Base 90. 2 87. 4 84. 6 80. 8 79. 0 Gals. butane/100 gals. base- 4. 2 7. 6 11.2 16. 4 19. 1
1d 2d 3d 4d 5d 10. 0 10. O 10. 0 l0. 0 l0. 0 4. 2 6. 9 9. 7 13.2 15.0 85. 8 83. 1 80. 3 76. 8 75.0 4. 9 8. 3 12. 1 17. 2 20. 0
A comparison of the data of blends containing 0 and 2% alcohol demonstrate the well known fact that alcohol tends to increase the vapor pressure of the base stock, requiring a substantial decrease in the butane base stock ratio if standard vapor pressure specifications are to be met. This required backing out of butane is especially per gallons of base, in the case of the Winter grade gasolines having Reid vapor pressure specifications of 13 p.s.i. or over.
On the other hand, comparison of data within any one type of blends having the same vapor pressure shows that as the alcohol content is increased above 4%, the hydrocarbon base stock can tolerate as much as or more butanes than in the absence of alcohol. Thus, the data of type 1 blends (summer grade-RVP 7.6 p.s.i.) show that the alcohol-free blend can tolerate 4.2 gals. butane per, 100 gals. base stock; with 2% alcohol this butane ratio drops rather abruptly to 3.4 gals. per 100 gals. base stock; but by using 6% alcohol the permissible butanes can be increased to the original value of 4.2 gals. per 100 gals, base stock; and by adding 10% alcohol the butane content can be increased further to 4.9 gals. per 100.
Similarly, inspection of the data on the type 5 blends (winter-grade; RVP 14.4 p.s.i.) shows that with 2% alcohol the gasoline may contain only 18 gals, butanes for each 100 gals, gasoline base stock; with 6% alcohol the butanes tolerance is increased to 19 gals. per 100, same as in the alcohol-free blend; and with 10% alcohol the permissible butanes are increased to 20 gals. per 100, a full point above the alcohol-free blend and two points above the blend containing 2% alcohol. Such increases are, of course, of great practical importance and demonstrate the great advantage of adding isopropyl alcohol to gasoline within the critical range of about 4 to.10%, and particularly in the range of 6 to 8%. As just demonstrated, this advantage is particularly outstanding in the case of the more volatile gasolines having Reid vapor pressures in excess of about 13 p.s.i.
While the data of Table III have been obtained using n-butane as the C component, results with mixed butanes and butenes would be very similar. For instance, isobuta'ne and isobutene raise the vapor pressure about 20% more than n-butane for the same amount added, butene-l about 10% more, and butene-2 same as n-butane.
EXAMPLE 3 The superiority of isopropyl alcohol over conventional gasoline-range U.O.P.'propylene polymer as an octane-improving additive is shown in Table IV in connection with a commercial premium grade hydrocarbon base stock. The same gasoline base was used in each test and contained 2.15 cc. of tetraethyl lead per gallon.
Table IV OOTANE VALUES 0F PROPYLENE DERIVATIVES IN GASOLINE large, about 1 gal.
of blend Heat of combus tron, B .t.u./gal.
percent None Prolglene polymer.
o Isopropyl alcohol The results show that the addition of 4% isopropyl alcohol results in an increase of about search octane number over the base gasoline used, and approximately another octane number can be gained by doubling the quantity of the oxy compound added. On a proportional basis this improvement is equivalent to an octane number of about 120 attributableto the alcohol additive alone. In contrast, the propylene polymer additive can be attributed an octane number of only about on a similar basis. Isopropyl alcohol in the form of organic mixtures such as those obtained by direct hydration of a similarly effective as the pure alcohol. The isopropyl alcohol similarly improves the Motor octane rating of of pure one Repropylene-containing hydrocarbon feed is proved by the addition because of octane number of gasolines for use in modern high-compression engines, the advantages, gained by the present invention cannot be over-emphasized, especially considering that by operating within the specified alcohol concentrations, the octane improvement is gained without having to displace the less costly butane fraction from the gasoline. The data also show that isopropyl alcohol has a great octane number advantage over propylene polymer which heretofore has been a favorite high-octane blending agent.
It is further interesting to note that the addition of as much as 8% of the alcohol lowers the heat of combustion of the gasoline by only about 1% as compared to the hydrocarbon base stock. This drop is essentially insignificant, particularly since it is accompanied by an octane number increase of almost two points. It will be realized, of course, that the value of a gasoline as an internal combustion fuel is determined not only by its heat of combustion, but also by the way in which it burns in the engine. Consequently, the octane number is usually a far more important characteristic of a gasoline than its heat of combustion. For instance, while n-heptane has a heat of combustion of 20,670 B.t.u./lb. and an octane number of 0, iso-octane has a heat of !combus tion of 20,540 B.t.u./lb. but an octane number of 100. Despite the somewhat lower heat of combustion of the iso-octane, the latter is obviously a far better and more economical motor fuel of the two. Accordingly, although the limited addition of the oxy compounds pursuant to the present invention reduces somewhat the heat of combustion, the resulting gasoline is nevertheless greatly imthe important improvement in anti-knock, starting, warmup and anti-stalling characteristics of the fuel. Moreover, this improvement can be obtained at a net saving in cost as compared with a conventional gasoline which contains propylene polymer instead of a hydration product as taught herein.
Of course, the fuel compositions falling within the,
scope of this invention may contain any of the commonly used gasoline additives. In particular these may include minor amounts of lead alkyl-anti-detonants, e.g. about 0.5 to 3 cc./gal. of tetraethyl lead, and the usually concomitant lead. scavenging agents. such as ethylene dibromide and dichloride, phosphate pre-ignition inhibitors such as tricresyl phosphate, various. dyes, gum or oxidation inhibitors such as 2,6-di-tert-butyl-4-methyl phenol, N- butyl-p-phenylene diamine or 1,4-diamino-dihydroanthraquinone, solvent oil, metal deactivators such as the N,N'- disalicylal-l,2-diamino derivatives of ethane or propane, and rust preventives such as sorbitan monooleate or various amine phosphates, nitrates or nitrites. It is apparent that the advantages of the invention in terms of high octane ratings, high butane utilization, good volatility distribution, and clean combustion can be obtained with all of the major types of gasolines including automotive, marine-type, as well as aviation gasolines.
Having described the general nature as well as specific examples of the invention, it will be understood that its ultimate scope is determined primarily by the appended claims.
What is claimed is:
1. A method of pressuring a motor fuel to a Reid I I I vapor pressure of about 13 to 15 psi. to form a final gasoline product having a Research octane number of at least 80, which comprises debutanizing a hydrocarbon base stock boiling in the gasoline boiling range and containing substantial amounts of 'catalytically cracked heavy naphtha boiling between about 300 and-420 R, depentanizing a reformed naphtha, mixing said naphthas, adding to said butane-free mixture 4 to 10% isopropyl alcohol and thereafter pressurizing said resulting mixture with 13 to 18% by volume of butane.
2. The process of claim 1 wherein 6 to 8% by volume of isopropyl alcohol is added to said motor fuel.
References Cited in the file of this patent Howes; pub. by John Wiley & Sons Inc., N.Y., 1935; vol. 1, pp. 119-l20; vol. 2, page 807. I n
Alcohol, A Fuel for Internal Combustion Engines, by Pleeth, Chapman & Hall, 1949, pp. 82-86.