Calculating Gasoline Blend OctAe Ratings W. F. SCHOEN AND A. V. MRSTIK Sinclair Research Laboratories, Inc., Harvey, I l l .
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T HAS always been the goal of refiners to predict accurately
the octane ratings of blended gasolines. Various methods utilizing the properties of the basic blending components, such as the linear or volumetric-type calculation, the Eastman technique (Y), and the Bogen-Nichols method ( 2 ) , have been employed for - . this purpose. However, since the advent of 90+ octane gasolines, it has become increasingly apparent that these methods are not adequate. Their use often results in predictions which are in error by more than two octane numbers when compared with . actual laboratory octane determinations. An improved technique for calculating both ASTM research and ASTM motor method octane ratings of blended gasolines is presented to overcome the deficiencies of present methods. The method is suitable for use with normal refinery gasoline blending stocks such as Fluid Thermofor and Houdry catalytic cracked gasolines, straight run gasoline, thermally cracked and thermally reformed gasolines, catalytic reformate, polymer, and alkylate. For stocks of this nature, the new tcchnique enables actane predictions for clear and leaded gasolines to be made with on accuracy approaching the reproducibility of ASTPII octane
determination methods. The octane numbers and olefin contents of the base blending stocks are the only data required for the utilization of the new method. EXPERIMENT DATA
I n order to derive the new technique, binary blends were made in 75/25, 50/50, and 25/75 volume ratio concentrations. The blending components used were typical refinery gasoline stocks consisting of straight run, catalytic cracked, thermally crarked, catalytic reformed, and thermally reformed gasolines, as well as polymer and alkylate. Inspection data obtained on the base components included octane ratings and volumetric olefin contents obtained by the ASTM D-875 method. I n spite of its known limitations, this method gave olefin values which correlated very well even in the case of high olefin Ftocks. T h e octane ratings, both clear and with 3 ml. tetraethyllead per gallon, obtained on the base stocks and on the binary blends were micromethod determinations. Binary blend data established base stock octane ratings, olefin contents, and composition to be the fundamental variables affecting blend octane ratings. An empirical correlation was established to evaluate the contributions of these variables. T h e validity of the method based on this correlation was substantiated by a series of multicomponent blends. METHOD FOR OCTANE PREDICTION
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The method involves handling all blends as a series of binary systems. First, the octanes of a blend of any t w a gasoline components are calculated volumetrically. T o the octanes thus derived, a blending appreciation factor (BAF) is applied. T h e binary blend calculated by this method is then treated as a single blending component in the next binary blend octane calculation with a third gasoline component. The procedure is repeated until all the individual gasoline componenb have been used to predict the octane of the final gasoline blend. The magnitude of the BAF to be applied t o each binary calculation is ascertained from the octanes and volumetric olefin content of the two components being blended, as well as the vol-
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BINARY OLEFIN DIFFERENCE
Figure 1.
Blending appreciation factor (BAF) for research octane ratings
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0 VOLUME % HIGH OLEFIN COMPONENT IN BINARY
Figure 2.
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B I N A R Y OLEFIN
Concentration correction factor for research octanes
Figure 3.
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DIFFERENCE
Blending appreciation factor (BAF) for motor method octane ratings
INDUSTRIAL AND ENGINEERING'CHEMISTRY
September 1955
ume percentage of these components in the binary blend. The value of the BAF t o be applied to ASTM research octane ratings, both clear and leaded, of 50/50 binary systems is plotted in Figure 1. The (BAF)&o,applicable to 50/50 volume ratio blends, is expressed as a function of the difference betu-een the percentage olefin content of the two blending components and of the octane
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THIS N E W TECHNIQUE for predicting octane ratings of blended gasolines
. . .enables predictions for clear and leaded gasolines with accuracies approaching reproducibility of ASTM octane determination methods
SAMPLE CALCULATION
Problem: Find the clear research and motor octane ratings of a blend made in the follo~r-ingcomposition using the base stocks shown.
Blend Component Catalytic cracked gasoline Straight run gasoline Thermally cracked gasoline
Vol. 7% In finished blend Olefins 50 65 40 0 10 40
. ..requires
as data only octane numbers and olefin contents of the base stocks
Clear Octane3 Motor Research 78 5 91 5 65 0 65 5 69 0 74 0
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difference between these stocks. The percentage olefin difference is always taken as a positive number. The octane difference of the two stocks is obtained by subtracting the octane of the low 1. Choose any two components for the first binary calculation, olefin component from the octane of the high olefin component and say the catalytic cracked and straight run gasolines. 2. Calculate linearly the octane rating and olefin composition map have eit,her a negative or positive value. of the binary blend, The BAF applicable to any Motor Method Research Octane concentration binary is derived Octane Octane from the (BAF)Soby use of the Vol. % in Blend Octane NO. x Octane No. X Vol. % 72 Olefin X Component Finished Binary No. Vol. % No. 1'01. % Olefins Vol. % correction factor (F) found in Catalytic cracked gasoline 50 55.6 78.5 43.6 91.5 50.9 65 36 F i g u r e 2. T h e c o r r e c t i o n 44.4 65.0 28.9 6 5 . 5 29.1 0 -0 Straight run gasoline -40 . factor (F) is a function of the 80.0 36 Totals 90 100.0 72.5 concentration of the high olefin 3. The octane and olefin differences between the catalytic component in the binary blend. cracked and straight run gasolines are determined, subtracting The BAF applicable to any concentration binary is obtained by the values of the low olefin component from those rf the high multiplying the ( BAF)50by- the appropriate correction factor ( F ) olefin component. Motor for that blend. Vol. % Method Researc h The BAF applicable t o motor method octane ratings of binary Stock Olefins Octane Octane blends may be calculated in the same manner as the BAF ap65 78.5 91.5 Catalytic cracked 0 65.0 65.5 Straight run plicable to the research octanes, by use of Figures 3 and 4. 4-65 f13.5 $26.0 Difference ' When calculating octane ratings of blended gasolines containing 4. ( BAF)60applicable t o a 50/50 composition blend of the two more than two components, the order of selecting stocks to be stocks being blended is then obtained from Figures 1 and 3 by calculated in a binary system is unimportant. The new method using the olefin and octane differences obtained in step 3. of predicting blended octanes will reproduce itself with a high Motor Research degree of accuracy irrespective of the order of calculation. HowOctane Octane ever, since base stocks containing the same percentage of olefin 5 0 / 5 0 BAF +3.0 +4 2 exhibit no octane deviation on blending, considerable time and 5 . The appropriate correction factor ( F ) is then obtained work may be saved by first calculating in one linear operation the from Figures 2 and 4,using the percentage of catalytic cracked octanes of a single blend containing all the components having gasoline in the binary blend, namely 55.6%. an equal concentration of olefins. Correction factor F for motor method octanes = 0.96 Correction factor F for research octanes = 0.99 6. By multiplying the (RAF)u obtained in step 4 by the corVALIDITY OF METHOD responding factor in step 5 , the BAF applicable to +he binary is obtained and added to the values obtained in step 2 as follows: On the basis of approximately 70 blends tested, the average Motor Research deviation of blend octanes calculated by the new technique and Method Method compared with actual laboratory determined octanes was 0.6 Octane Octane octane. This deviation was based on motor method and reBinary blend (step 2) 72.5 80.0 BAF (step 4 X step 5) +2.9 +4.2 search octanes, clear and with 3 ml. tetraethyllead per gallon, 75.4 84.2 Binary octanes of Blend I for each of the 70 blends. Based on the linear method of calcu7 . The binary blend obtained is then used as a basic blending lation, the deviation for the same blends was 1.5 octanes. component and is blended with the remaining components in a The value of the binary-type similar manner. blending method becomes inSolution:
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Stock Blend I Thermal gasoline Linear totals Olefin differenre. 7% Octane difference 5 0 / 5 0 (BAF)so (Figures 1 and 3 ) Correction factor (F) BAF applicable t o binary Predicted octanes of finished blend
Composition 90.0 10.0 100.0
... ,..
...
... ...
Olefins 36 40
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4
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Motor Method Octane Octane Octane No. No. X % 75.4 67.9 69.0 __ 6.9 ... 74.8
... ... ... ...
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-6.4 -0.1 0.49
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Reseamh Octane Octane Octane NO. KO.X % 84.2 75.8 74.0 __ 7.4 ... 83.2
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c r e a s i n g l y pronounced when dealing with blends containing high concentrations of components having large olefin and octane differences. When blends of this type are calculated in a linear fashion, the predicted octane ratings are generally in c o n s i d e r a b l e error. For ex-
I N D U S T R I A L , ’A N D E N G I N E E R I N G C H E M I S T R Y
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Vol. 47, No. 9
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Figure 4.
Concentration correction factor for motor method octanes
ample, the average of the ten highest deviations of linear calculated octanes compared to actual laboratory determinations was 6.0 octanes for the blends studied, the predicted octanes being low in all cases. B y use of the new blending technique, a similar average for the ten highest deviations was 2.0 octanes, distributed evenly between high and low predictions. On Figure 5 the deviations of the calculated octane ratings from the actual octane determinations for both the new and the old linear method of octane prediction are plotted as probability functions. The resultant curve for the new method of calculation is a straight line, with the 50% point crossing a t zero deviation. This line indicates t h a t the deviations by the nev method essentially follow a normal distribution about the zero deviation point. It may also be noted from this curve that approximately 85% of the calculated blend octanes are within 11.0 octane numbers of the laboratory octane determinations. The octane rating reproducibility established by the ASTM ( 1 ) indicates that determinations will be within 11.0 octane number of the true octane rating approximately 90 t o 95% of the time. On this basis i t may be concluded that the reproducibility of the new method of calculating blended octanes is almost equal t o the reproducibility of the laboratory determinations. The probability curve obtained for the linear method devix-
. 0.1 I 5 IO 20 40 60 80 SO 95 989999.5 ACCUMULATIVE PERCENT OF TOTAL DEVIATIONS
Figure 5.
Probability plot of octane deviations
tions is concave downward indicating a distribution skewed toward the negative deviations. This curve indicates that the median of the deviations is a t -0.7 octane. Only 49% of the deviation points lie within the zk1.0 octane deviation area, indicating some factor other than normal octane reproducibility is affecting the octane deviations obtained by use of the linear method of calculation. The new method was developed primarily t o enable accurate blend calculations t o be made in order t o establish the most advantageous refinery blending procedures. It has also been of considerable aid in research case studies. However, it should be emphasized that the method was developed for use with normal refinery gasoline blending streams, and any extrapolation of this technique to pure components or select cuts of normal stocks may possibly result in erroneous octane calculations. LITERATURE CITED
(1) American Society for Testing Materials, Philadelphia,
Pa., “Manual of Engine Test Methods for Rating Fuels,” 1952. (2) Bogen, J. S., and Nichols, R. &I., IND.ENG.CHEM.,41, 2629 (1949).
(3) Eastman, Du Bois, Ibid., 33, 1155 (1941). RECEIVED for review November 8, 1954.
ACCEPTED May 2, 1955.
Kinetic Study of the Steam-Carbon Reaction. INFLUENCE OF TEMPERATURE, PARTIAL PRESSURE OF WATER VAPOR, AND NATURE OF CARBON ON GASIFICATION RATES J. 11. PILCHER’, P. L. WALKER, JR., AND C. C. WRIGHT2 T h e Pennsylvania S t a t e University. University Park. Pa.
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ORDER to improve methods for t h e gasification of solid fuels, fundamental information is needed concerning t h e rate and mechanism of t h e steam-carbon reactions. T h e literature contains a number of papers ( 1 , 5-7, 9, 10,12, IS, 15, 61,12) concerned with the kinetics of these reactions, but t h e reports by various investigators are in many respects contradictory and confusing. For example, t h e order of the reaction with respect to steam has been reported by different authors as negative, 1 1
Present address, Battelle Memorial Institute, Columbus, Ohio. Deceased.
zero, fractional, first, second, or unknown. Gadsby, Hinshelwood, and Sykes (6) account for much of the disagreement on t h e basis that t h e retarding effect of hydrogen is often overlooked in determining the reaction order. -4 wide variation in t h e type of carbon studied, ranging from coal to graphite, undoubtedly also has had a major effect on the inconsistencies of t h e results. Regarding the mechanism of t h e reaction, it has been shown rather conclusively in two recent papers, one by Long and Sykes ( 1 3 ) and one b y Johnstone, Chen, and Scott ( 9 ) , t h a t the primary product of the reaction between carbon and steam is carbon
