I
S. C. SAMUELS, G. C. RAY, and A. D. REICHLE Phillips Petroleum Co., Bartlesville, Okla.
High Octane Components from Catalytic Reformates High octane components can be produced in substantial yields from typical catalytic reformates by fractionation, solvent extraction, selective adsorption, and selective cracking. Process equipment and product properties are markedly different for each process. A simple and direct comparison is precluded by their highly individual characteristics and range of applicability.
THE
trend in automotive engine design and the competitive gasoline market are continually forcing octane numbers higher. Research octane numbers of 102 to 106 for the average premium gasoline are forecast for 1961 (7, 3 ) ; already superpremium grades having octane numbers above 100 are being marketed. Catalytic reforming, with its 14 process versions, has played a major role in producing these fuels-at present 30% of the gasoline produced in the United States is obtained by this process, and it is predicted that its percentage will rise to 45 by 1960 ( 2 ) . The steady pressure of the octanenumber race requires optimum utilization of catalytic reforming processes and products. Substantially increased octane numbers can be obtained by raising the severity of reforming conditions, but decreased yield and catalyst life result primarily from hydrocracking of paraffins to nongasoline-range materials. The resultant increase in aromatics concentration is the principal cause of observed octane number increase. A number of methods can be used with catalytic reforming to increase octane number without severe reforming-e.g., fractionation, solvent extraction, selective adsorption, and selective cracking, which separate or concentrate high octane components. Each of these separation procedures has been applied to typical catalytic reformates.
Apparatus and Procedure The feedstocks (Table I) were typical catalytic reformates from straight-run fractions. Research octane numbers (RON) ranged from 90.3 to 98.7, plus 3 ml. of tetraethyllead (TEL) per gallon. The reformates were fractionated
are Research octanes f 3 ml. of T E L per gallon unless otherwise stated.
batchwise in a 30-plate Oldershaw laboratory column using a 5 to 1 reflux ratio. The volume of each cut was 10% or less of the original. A similar 15plate Oldershaw column was used for splitting reformates into light and heavy fractions. Batch equilibrium solvent extractions were carried out in separatory funnels or stainless steel pressure mixing vessels. A Podbielniak centrifugal countercurrent extractor was used for continuous extractions with diethylene glycol. Continuous sulfur dioxide extractions were made in an 8-foot countercurrent extraction column consisting of a 6-foot contacting section, 2 inches in inside diameter, fitted with perforated plates at 6-inch intervals and a 2cfoot enlarged lower section, 3 inches in inside diameter, for disengaging entrained raffinate. Laboratory scale columns packed with granular Linde 5A Molecular Sieves were used for selective adsorption experiments in both liquid and vapor phases. The adsorbate was recovered by heating the system under vacuum or heating while purging with a n inert gas. The bench scale thermal cracking unit consisted of a Bosch pump, a coil made of stainless steel tubing g/la inch in diameter, approximately 35 feet long, an electrically heated furnace, and a product accumulator. The depth of cracking was controlled by varying the coil outlet temperature from 925’ to l l O O o F. A constant cold oil velocity of 3 to 4 feet per second was maintained in all runs. Pressure levels were 50 and 500 p.s.i. The octane numbers hereinafter given
Table 1.
Fractionation. Fractional distillation of catalytic reformates into small cuts produced a series of fractions with a wide range of properties (Table 11). The lowest boiling 10% fraction from a 94 octane reformate had an octane number of 96.8. Several middle boiling range cuts had octane ratings of 99. Cuts with relatively low octane numbers (85 to 91) were present on either side of these fractions. The highest boiling fractions were characterized by octane ratings of 100 or higher. This distribution of octane numbers is typical of catalytic reformates from straight-run naphthas. With the exception of the light ends, there is a good correlation between octane rating and aromatics content (Figure 1). Separation of the middle high-octane fractions from the adjoining less desirable fractions would require extensive fractionation facilities. The general concentration of aromatics in the higher boiling fractions indicates that simple splitting would segregate a high octane component, This type of operation is illustrated in Figure 2 for three reformates with octane numbers ranging from 91.1 to 98.7. A 40 volume % yield of heavy reformate having an octane number of 104.2 can be obtained by splitting a 98.7 octane reformate. When the octane rating of the reformate is 90 or lower, only a 10 volume % yield of heavy reformate having an octane of 100 can be obtained.
Feedstocks Were Typical Catalytic Reformates from Straight-Run Fractions
ASTM distillation, IBP
O
A
€3
Stock C
D
113 207 272 332 389 4.8 51.0
118 196 268 320 390 4.6 52.0
117 185 264 328 387 3.9 50.5
105 163 256 324 395 6.0 52.6
... ... ... ...
50.5 1.7 12.0 35.8
45.8 1.4 9.0 43.8
44.1 2.2 12.6 41.1
52.8
76.3 91.1
83.1 94.2
84.5 95.3
91.5 98.7
E
F.
10% 50% 90%
E.P. Reid vapor preisure, lb. Gravity, OAPI at 60° F. Composition, vol. yo Paraffins
Olefins Naphthenes Aromatics Research octane number Clear 3 ml. TEL/gal.
+
Results
...
90.3
VO1.’51, NO. 1
115 179 275 334 411
...
47.6
... ... ...
JANUARY 1959
73
110
1
I
I
I
1
100
90 80
1
I
100
I
I
I
I
1
105
100
95
90
0 -
20
0
60 VOLUME % DISTILLED 40
I
I
80
100
Figure 1. Correlation between octane rating and aromatics content i s good
Simple splitting of catalytic reformates produces heavy blending stocks having an octane number of 100 or more in yields directly related to the octane number of the original reformate. The lighter and lower octane number fraction from this operation can be used directly as a blending stock or upgraded by recycling to catalytic reforming, additional fractionation, etc. Extraction. Another approach to upgrading catalytic reformates is liquidliquid extraction with a suitable solvent for separation of aromatics from saturates. The potentialities of this type of separation are best illustrated \vith rela-
Table II.
Fraction
Stock C
100
5 6 7 8 9 10 11 Bottoms
Loss
Table 111.
~ ~ i Range.
F. 117-387
5.03 4.81 9.72 9.96 9.87 9.88 9.78 9.84 9.91 9.91 4.95 5.77 0.57
...
...
140-187 187-215 215-231 231-260 260-282 282-285 285-322 322-338 338-361 361+
Olefins
+
Aromatics Research octane number Clear 3 ml. TEL/gal.
74
20
tively pure aromatic and saturate fractions from a typical reformate. To ascertain the ultimate properties to be expected from any highly selective separation process, deisohexanized stock D (topped to 140" E'. still head temperature) was separated into aromatic and saturate concentrates by silica gel elution chromatography (Table 111). The saturates were eluted with n-pentane and the aromatics with methanol. \2'ith this particular stock, a 47.2 volume % yield of blending stock of 110.4 octane number was obtained. I t is apparent that aromatic extracts of about this same high quality can be obtained
Research iOctane ~ ~ Yo.~ Par+3 ml. affins, Olefins, Clear TEL/gal. Vol. 7G Vol. 83.1
94.2
45.8
89.6 78.9 73.2 64.0 88.3 66.0 82.0 92.5 80.0 94.7 99.1 104.1
99.0 94.5 91.0 84.5 99.2 85.6 94.8 98.8 91.5 99.8 103.0 107.0
99.1 95.6 67.2 63.6 34.5 55.9 43.3 30.4 39.7 25.2 15.5 1
1.4
... ...
1.0 1.4 1.2 1.6 1.4 1.0 1.8 1.8 1.5 4
Naphthenes, 1'01.
dromatics,
T'ol. %
9.0
43.8
0.6 3.6 21.9 23.9 12.6 11.3 8.3 5.6 6.9 3.0 2.3 5
trace 0.8 9.7 11.1 51.7 31.2 47.0 63.0 51.6 70.0 80.7 90
Charge Stock
Aromatic Fraction
Saturate Fraction
100.0 47.0
47.2 30.4
52.8 64.4
50.0 2.4 47.6
1.2 0.9 97.9
94.7 2.5 2.8
83.0 95.1
107.4 110.4
42.2 69.6
INDUSTRIAL AND ENGINEERING CHEMISTRY
40 60 BOTTOMS PRODUCT, VOLUME %
80
100
Figure 2. Simple splitting of higher boiling fractions segregates a high octane component
Silica G e l Chromatographic Separation of Deisohexanized Stock D Gave a Blending Stock of 1 10.4 Octane Number
Yield, vol. yo Gravity, OAPI Composition, vol. % Parafins naphthenes
+
l
I
L _ _ i _ - - _ L - - - A - i 0
Fractional Distillation Produced Fractions of Widely Varying Properties
Feed Vol. %
1 2 3 4
85
from an efficient extraction process in yields equal to or less than the original reformate aromatics content. Higher extract yields can be obtained at the sacrifice of octane number. Batch equilibrium separations were carried out with seven solvents which previous experience had indicated were capable of effecting a good separation. Solvent ratio, extraction temperature, and in some cases, water content, were varied over a considerable range. Caralytic reformates containing 41 to 50% volume of aromatics and with leaded Research octane numbers of 94 to 95 were used. Solvents were first compared on the basis of selectivity for separating aromatics from nonaromatics. Selectivity is defined as: (VAE)(VNR)/(VNE) (V.iR), where V = volume fraction of component denoted by first subscript, either aromatics, '4, or nonaromatics, N: i n the product indicated by the second subscript, extract E or raffinate R . Selectivities and the range of experimental conditions for seven solvents are shown in Table I\'. Over the range of conditions studied, sulfur dioxide had the highest selectivity; diethanolamine, diethylene glycol, and dimethyl sulfoxide have moderate selectivity, but are not in the same range as sulfur dioxide. Of almost equal importance in the evaluation of a solvent is its solvent power. Sulfur dioxide is superior to the other solvents in this respect also. Methanol has a high solvent power, but its selectivity is low. O n the basis of selectivity and solvent power, sulfur dioxide and diethylene glycol were chosen for further study in continuous extraction apparatus (Table V). Because sulfur dioxide forms azeotropes with most C6 hydrocarbons, a low boiling fraction was removed from the two reformates used in continuous extractions with this solvent. High octane extracts are produced in good yield with sulfur dioxide at low
HIGH OCTANE FUELS I
60
0
20
40 60 80 AROMATICS CONTENT, VOLUME %
too
Figure 3. Estimation of extract and raffinate yield-octane number relations is made easier by correlation of aromatics content and octane number
solvent-oil ratios of 0.7 to 0.9. A deisohexanized reformate having a Research octane rating of 95.1 produced a n extract having a rating of 98.9 at a yield of 79 volume %. Starting with a 90.0 leaded Research rating, the yield of extract of 100.7 octane number was 55.8 volume %. Diethylene glycol requires a considerably higher solvent-oil ratio; however, substantial yields of extracts with octane number above 100 are readily obtained. With a debutanized
Table
IV.
85 85
Figure 4.
90 95 RAFFINATE YIELD, VOLUME X
Molecular Sieve treatment of catalytic reformates
reformate of 94.7 leaded Research rating, a 56.5 volume % yield of extract of 103.7 octane number was obtained a i a 5.5 solvent-oil ratio. Research octane numbers of the raffinates from liquid-liquid extractions ranged from 68 to 78. If these raffinates are to be recycled to the reforming step, the selectivity need be only high enough to produce a n extract with the desired octane number; if the raffinates are to be used as low aromatic content sol-
Batch Equilibrium Separation of Catalytic Reformates Water, VOl. % 5-20
Table
4.5-10
... ... ... ... ...
V.
Temp., O F. 35-75 120 60 300-400 79-350 60 0-(-38)
Solvent Ratio 1.0-4.0 3.5-5.7 0.8-3.0 2.5-6.2 1.0-4.0 0.6-3.0 2.9-3.3
Selectivity 2.O-5.0 2.9-5.3
4-5 4.8-7.9 3.0-9.1 9-14 16-61
Extraction of Catalytic Reformates
Sulfur dioxide produces high octane extracts in good yield
Aromatics, vol. % RON 3 ml. TEL/gal. Extraction conditions Solvent ratio Temperature, O F. Extract Yield, vol. % Aromatics, vol. % ’ RON f3 ml. TEL/gal. Raftinate Aromatics, vol. % RON f3 ml. TEL/gal.
+
Diethylene Glycol, Podbielniak Centrifugal Sulfur Dioxide, Perforated Plate Column Extractor, Deisohexanized Deisohexanized Debutanized stock D stock B Stock D 43.2 47.6 38.9 95.1 90.0 94.7
0.7
0.Q
5.5 259
79.0 58.6 98.9
55.8 67.8 100.7
56.5 68.8 103.7
2.7 68.0
2.3 66.0
9.3 78.0
- 13
- 15
100
Gains in leaded research octane number resulted from removal of n-paraffins
Over the range of conditions studied, sulfur dioxide had the highest selectivity and solvent power
Solvent Methanol NHs Phenylethanolamin e Diethanolamine Diethylene glycol Dimethyl sulfoxide Sulfur dioxide
I
vents, jet fuel components, etc., high selectivity with respect to aromatics content of the raffinate is required. Estimation of extract and raffinate yield-octane number relations is facilitated by the use of aromatics contentoctane number correlations. The curve of Figure 3 is based on 58 reformates and on extracts and raffinates from these reformates with a range of aromatics contents from 2.8 to 97.9 volume %. There is a considerable deviation from linearity. If the quality (octane number or aromatic content) of the reformate is known, for a raffinate of any selected quality, the yield of extract of any desired octane number can be calculated from a n aromatics balance and the aromatics content-octane number correlation. Selective Adsorption. The content of n-paraffins in catalytic reformates depends on feedstock composition and reforming severity. Typical reformates ’ as n-paraffins. contain up to 15 volume % Removal of n-paraffins, which have characteristically low octane numbers, would increase octane number considerably. .Molecular Sieves are well suited for this purpose. These adsorbents possess a relatively narrow range of pore sizes and are able to adsorb molecules selectively on the basis of their size and shape -hence the name Molecular Sieves. Preliminary experiments with mixtures of pure hydrocarbons demonstrated the high selectivity and capacity of Molecular Sieves for selective adsorption of n-paraffins. Next, several catalytic reformates of full boiling range were treated in laboratory scale columns with Linde 5A Molecular Sieves. Gains in leaded Research octane number of 0.43 to 0.54 number for each per cent of VOL. 51, NO. 1
JANUARY 1959
75
Figure 5. Selective thermal cracking of 95.1 octane number, catalytic reformate, increases aromatics contentand octane number
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75
80 85 90 95 Cg f GASOLINE, VOLUME % OF CHARGE
n-paraffins removed were obtained (Figure 4). In each case n-paraffins were completely removed by a proper choice of conditions. As would be expected for n-paraffin concentrates, the leaded Research octane numbers of the adsorbate varied from 50 to 64. Maximum octane number increase would be expected for fractions with a high n-paraffin content. As a n extreme example, removal of the 22 volume % n-paraffin content of a low boiling reformate fraction increased the leaded Research rating from 81 to 91. Molecular Sieve treatment will increase the octane rating of the higher boiling reformate fractions. Removal of 370 volume of n-paraffins from a 275" F.+ reformate fraction increased the octane number from 105.5 to 107.2. Selective Thermal Cracking. The aromatics content and octane number of catalytic reformates can be increased by thermal cracking. I n general, thermal cracking rates of n-paraffins are higher than the cracking rates of the more desirable isoparaffins, naphthenes, and aromatics. Thus, aromatics can be concentrated by removal of n-paraffins as fragments boiling outside the gasoline range. Selective cracking tests were carried
100
out with a deisohexanized catalytic reformate from stock D (Table I). A light fraction, C5-iso-Cs, was removed from this stock prior to the cracking tests, because it had a high octane number (96.5) and was least likely to be upgraded by thermal cracking. Yield-octane number relations from low pressure (50 p.s.i.g.) and high pressure (500 p.s.i.g.) thermal cracking of this deisohexanized stock are given in Figure 5 and Table VI. At 100 octane number, C j + product yield is 84.5 volume % for the low pressure operation and 87.5% for the high pressure operation. Octane number from selective cracking is improved by increasing both the net quantity and the concentration of the aromatics. The latter is the result of formation of light components boiling outside the gasoline range. At low thermal severities, concentration is the predominant effect (Table VII). Cracking of nonaromatics at low severity to C* and lighter products resulted in a n aromatics content of 56.9 volume %; a n additional 1.6% was apparently produced by thermal dehydrogenation of naphthenes. Concentration effects alone would have produced a n aromatics concentration of 63.7% a t high severi-
Table VI. Selective Thermal Cracking o f 95.1 Octane Number, Catalytic Reformate
Table VII. High Pressure (500 P.S.I.G.) Thermal Cracking o f 95.1 Octane Number Catalytic Reformate
At 100 octane number Cs+ product yield Is 84.5 volume % for low pressure and 87.5 % for pressure operation Pressure, P.S.I .GI 50 500 Yields Cz and lighter, wt. % 6.5 4.2 Ethylene, wt. yo 2,8 1.2 Ethane, wt. yo 0.4 1.6 Propylene, vol. % 6.3 4.3 Propane, vol. % 0.7 2.2 Butenes, vol. % 3.3 2.7 Butanes, vol. % 0.3 0.9 CS+ gasoline, vol. % 84.5 87.5
At low thermal severities, concentration is the
+ 3 ml. TEL/gal., CS+ gasoline
RON
76
100.0
100.0
predominant effect Cs -k Product from to Thermal Cracking Thermal Low High Cracking severity severity
ties. The additional 8% resulting in a final aromatics concentration of 71.7% is attributed to dehydrogenation of naphthenes. Fractionation, solvent extraction, and selective adsorption split the reformate into liquid streams of high and low octane number. Thermal cracking produces a single liquid stream of high octane number and an unsaturated gaseous product (Table \.I). Alkylation and/or polymerization of the light olefins can be used to obtain additional components of high octane number. For the 500 p.s.i.g. operation producing C,+ thermal reformate with a 100 leaded Research octane number. polymerization of the Ca and Cd olefins results in a 6.3 volume % yield of the same quality gasoline. Alkylation of these olefins produces a 10.7 volume 70 yield of 105 octane number motor alkylate. At a pressure of 50 p.s.i.g. where CS and C4 olefin yields are higher, the use of polymerization and /or alkylation will offset the lower gasoline yield. In addition to the higher yield of gasoline and improved Research octane number obtained by addition of alkylation of the light olefins, this route significantly decreases gasoline sensitivity. Combined yields from the selective crackingolefin processing combination are shown in Table VIII. Both routes produce of 100 high yields, 94 to 98 volume 70, leaded Research octane number gasoline.
Table VIII. Selective Thermal Cracking Plus Olefin Processing Produces High Yields of 100 Leaded Research Octane Number Gasoline Selective Cracking
Plus olefin polymerization
Plus olefin alkylation
Yields, T'ol. yo,Basis C,+ Catalytic Reformate
Cs-iso-Ce removed from catalytic reformate CS+ from thermal cracking Polymer gasoline Motor alkylate Total Cs+ gasoline RON 3 ml. TEL/ gal.
+
8.1
8. 1
79.9 5.8
79.9
*.. 93.8 99.7
...
~
9.8 97.8 100.2
Charge
Composition, vol. % Paraffins 39.6 Olefins 2.4 Naphthenes 10.4 Aromatics 47.6 Yield, vol. % 100.0 RON 3 ml. TELjgal. 95.1
INDUSTRIAL AND ENGINEERING CHEMISTRY
+
27.5 6.6 7.4 58.5 83.9
18.9 6.7 2.7 71.7 75.0
101.5
104.4
Literature Cited
.ry, S. W., Petrol. Refiner 36, No. 5, 2 (1957). xey, J. G., Jr., Zbzd., 35, No. 5, 1956). 1. Petrol. News 49, No. 7 , 150 RECEIVED for review February 5, 1958 ACCEPTED September 22, 1958
Southwest Regional Meeting, ACS, Tulsa, Okla., December 1957.
