Naphthas from Fluid Catalyst Cracking C. E. STARR, JR., J. A. TILTON, AND W. G. HOCKBERGER Esso Laboratories, Standard Oil Company of New Jersey, Louisiana Division, Baton Rouge, La.
tically timed. Ten-liter charges were segregated through this equipment into fractions of C, and lighter hydrocarbons, gasoline, and bottoms products boiling higher than gasoline. The fractions of C, and lighter hydrocarbons were then distilled through Podbielniak Hyd-Robot automatically controlled columns for the segregation of Cq fractions, which were then analyzed by infrared absorption spectra measurements. The naphthas were distilled by precise fractionation through helix-packed columns of about 100 theoretical plates and with 20 to 1reflux ratio. Xarrow-boiling fractions (usually 2 volume yo of charge) were segregated. Charges to these analytical distillation columns yyere 4000 ml., so that the resultant narrow fractions would amount to about 80 ml. The boiling points of these narrow fractions were obtained by Cottrell distillation. Analyses were made by refractive index measurements and gravity, . . boiling - point, _ . and bromine number determinations. The olefin content was calculated as mono-olefins from a modified Francis bromine number (6) by the following formula:
T h e compositions of naphthas derived from cracking with Fluid Catalyst vary within wide limits depending upon changes in operating conditions, types of catalyst employed, and feed stocks used. The compositions of nine naphthas are presented to illustrate the types of products obtained at low and high cracking temperatures with varying cracking severities, employing clay and synthetic catalysts with several paraffinic and naphthenic feed stocks. Composition data show that a number of valuable hydrocarbons, such as toluene, are present in the cracked naphthas to an extent which makes feasible their removal. The flexibility of the Fluid Catalyst cracking process permits operations for production of high quality fuels concurrent with a number of hydrocarbons that are individually valuable as raw materials for chemical manufacture.
Wt. % olefins = bromine number
T
HE versatility of the Fluid Catalyst cracking process permits wide variation of product composition. Use of cracked hydrocarbons as raw materials for chemical manufacture has necessitated detailed hydrocarbon analyses of the naphthas and light ends products. Composition studies augment the usual process and quality data and provide a basis for planning treatments t o make naphtha products suitable for special uses, such as in aviation fuels. Composition studies also establish the yields and concentrations of specific hydrocarbons, such as toluene and other relatively low boiling aromatics, and certain valuable light hydrocarbons; the latter include isobutane, isdbutylene, and normal butenes, which are employed in alkylation processes for the production of aviation fuels of high octane number and in chemical processes for the production of synthetic rubber. Studies were made of the composition of more than 100 naphthas representing a wide variety of conditions encountered in the Fluid Catalyst cracking process. These conditions comprised operating temperatures of 750-1000 O F., feed stock conversions of 35-90%, clay and synthetic catalysts, and low and high boiling naphthenic-type and paraffinic-type feed stocks. Process data for such operations have been described in the literature (3, IO, fl), as have data for the quality of the Fluid Catalyst-cracked products (9). Compositions of nine typical naphthas, selected to represent a n ide variation in operating conditions, are presented in this article. Previously published articles regarding the composition of catalytically cracked gasoline dealt n4th products from the Houdry fixed-bed process. One paper ( 2 ) concluded that the high octane number of catalytically cracked gasoline is due to the presence of a large excess of isoparaffins over normal paraffins in the lower boiling portions of the gasoline, and t o a high content of aromatic hydrocarbons in the higher boiling fractions. Another paper (1) related the effects of feed stock boiling range and of cracking severity to the composition of the cracked gasoline.
weight x molecular 160
The aromatic hydrocarbon content was determined by means of the specific dispersion, corrected for olefin content, according to the method of Grosse and Wackher ( 7 ) . The specific dispersion was calculated by the following formula:
NF
- Nc x
din
104
where NF = refractive index of hydrogen F line (4861 Angstrom units) N c = refractive index of hydrogen C line (6563 Angstrom units) The refractive index measurements were made with a Bausch & Lomb precision refractometer. The correlations for aromatic hydrocarbon content were chebked in a number of instances by removing aromatics by extraction and adding back known amounts of aromatics t o aromatic-free stocks of different compositions. The naphthene hydrocarbon content was arbitrarily designated to include both cycloparaffins and cyclo-olefins. I t was determined by means of the specific refraction according t o the LorenzLorenta formula:
v2-1 Nj$72
1
xp
where N = refractive index of sodium D line (5893 Angstrom units) The naphthene content was determined on the basis of all naphthenes having an average specific refraction value of 0.3300, whereas the average specific refraction of paraffins varies from approximately 0.3380 for a boiling point of 400' to approximately 0.3500 for a boiling point of 100' F. Specific refractions of cracked naphtha cuts must be corrected for the effect of olefins, including cyclo-olefins and also for the effect of aromatics. After correction the specific refractions of cyclo-olefins in the 100-400" F. boiling range approximate 0.3300 fairly closely, and the specific refractions of acyclic olefins approximate the values for the corresponding paraffins. Consequently, cyclo-olefins are included once as part of the naphthenes and a second time as part of the olefins, without being determined directly as cyclo-olefins. Paraffins cannot, therefore, be determined as the difference between 1007, and the sum of aromatics plus naphthenes plus olefins. I n the analysis of catalytically cracked naphthas the practice was adopted of reporting one composition giving the acyclic-cyclic division and another giving the olefin-nonolefin division: (a) 7,aromatics % naphthenes acyclics =
METHODS OF ANALYSIS
Total cracked products were distilled in glass stills of approximately twenty-five theoretical plates a t 10 to 1refluxratio. These stills had columns packed with 3/32-inch metal helices. The pots were of 12-liter capacity, and the reflux regulation was automa-
+
19s
+ r0
INDUSTRIAL AND E N G I N E E R I N G C H E M I S T R Y
196
SAMPLE NO. 1
Vol. 39, No. 2:
SAMPLE NO. 2 FEED: T E M PER A T U R E,O E:
FEED: TINSLEY GAS OIL 800 T E M PERATURE,oE: C O N V E R S I O N , VOL.70: 49
TINSLEY GAS Oil. 975
460
380
L" 0
300
and of o-qrlene 292.1 O F. Separat'ion by straight distillation is not practicable. In this study no attempt n-as made to effect analyses for the individual Cs aromatics in t'he naphthas from the paraffinic feeds. The concentrations of CSaromatics in narrow fractions from the naphthas from severe cracking of the Tinsley gas oil, or from moderately severe cracking of the lover boiling East Texas kerosene, are as high as 85 to 98 volume %. The Cs aromatics are useful as high octane number blending constituents or as solvent's. o-Xylene, which is estimated at about 25 volume % of the Cs aromatics, has use as a raw material for the production of phthalic anhydride. NAPHTHENES. Data given in Table 11 illustrate that, in general, the highest concentration of naphthenes occurs in the 200250" F. fractions of the naphthas from the paraffinic feed stocks. Yaphthene concentrations are highest when cracking severity is low; when cracking severity is high, the naphthenes in the fiaction3 above 200 O F. disappear in favor of increased aromatic. content. The composition data shov that the concentration of naphthene; is quite constant in the 115-200" F. fractions, regardless of the cracking severity and whether silica-alumina catalyst or clay catalyst is used. The l o x boiling East Texas kerosene yieldt B cracked naphtha having relatively higher naphthene concentrations in the 115-200" F. range. Table IV lists the yields of CbrCs, and CT naphthenes that niay be readily identified by the methods of annlyqis employed in thi. study. The cycloparaffin yields necessarily include the come Fponding cyclo-olefinb. Cyclopentane (boiling point, 120.6O F.; yields on feed are low, from 0.1 to 0.4 volume %. The data in Figures 1 and 2 also show that the concentrations in narrow fractions are low, the highest being 33 volume % for one fraction 111 3ample 3
TABLEIT. YIELDSOF NAPHTHENES~ FROBI PARAFFINIC PEED STOCKS Sample No. 1 Yield, vol. % on feed Cyclopentane 0.1 llethylcyclopentane cycio1.0 hexane DimethvlcvcloDentanes 0.8 Methylcydohexane 4- ethylcyclopentane 0.9 2.8 Total * Includes any cyclo-olefins present.
+
-
2
3
4
5
0.2
0.4
0.2
0.1
0.9 0.7
0.8 0.4
1.1 0.9
1.2 0.7
0.4
L 8 3.0
= 2.4
2.0
= 2.7
The yields on feed of inethylcycloperitane (boiling point, 161.3" F.) and cyclohexane (boiling point, 177.4" F,) are reported together in Table IV. They vary from 0.8-1.2 volume % for tlw
group of naphthas from paraffinic feeds. Figure 1 illustrates that, in the case of sample 5 from East Texas kerosene, the methylcyclopentane plus cyclohexane concentration is as high as 60 volume % in the narrow fractions. The boiling points of the 2% fracTOLUENE, AYD CS AROM.YI~IC~ TABLE 111. YIELDSOF BENZENE, tions indicate that methylcyclopentane predominates over cycloFROV P 4 R 4 F F I N I C FEEDSTOCKS hexane. Calculated equilibrium compositions for a binary methSample No 1 2 3 4 5 ylcyclopentane-cyclohexane system show 90% methylcyclopenYield, vol. % on feed 0.41 0.39 0.19 Benzene 0.07 0.29 tane at 800 O F. and 93v0 methylcyclopentane at 1000' F. 2.45 2.49 1.44 Toluene 0.62 1.51 Bimethylcyclopentanes include the 1,l-isomer which boils at Cs aromatics 1.71 3.39 4.72 3.75 5.21 Total 5.19 7.60 6.38 8.07 2.40 189.5' F., the 1,2-isomer~having CLS and trans forms which boil a t 211.6" and 197,4OF., respectively, and the 1,3-isomerq, whic'i include a trans form boiling at 195 6' and a cis form probably Toluene yields range from 0.6 to 2.5 volume % on feed, value, $oiling a t about 195' F. The yields of dimethylcyclopentanes roughly six time5 as great as the benzene yields. Toluene, like wported in Table IV comprise the naphthenes content of the benzene, tends to distill overhead below its boiling point (231.2 O narrow frartions boiling between 180-205' F. The yields on feed of climethglcyclopeiitaiies amount t o 0.4-0.9 volume %. F.) ; however, because of the higher proportions of toluene, it is relatively easier to concenttate. Figures 1 and 2 show that narYields of methylcyclohexane (boiling point 213.4" E' ) anu row fractions contain as high as 86 volume %toluene. ethylcyclopentane (boiling point 217.6 O F.) are reported toYields of xylenes plus ethylbenzene vary from 1.7 to 5.2 volume gether in Table IV and vary between 0.4-0.9 volume % for the yoon feed; these yields are roughly 2 t o 2.5 times as great as toluparaffinic feed stocks. The detailed composition data for the
naphtha from the low boiling feed stock (sample 5 , Figure 1) show the presence of narrow fractions Containing as much as 62 volume yoof methylcyclohexane plus ethylcyclopentane. PARAFFINS AND OLEFINS. These hydrocarbon types have not been completely differentiated by the analytical procedure employed. Unsaturated naphthenes are determined both as olefins and as naphthenes; therefore any estimation of paraffins by subtracting mono-olefins from per cent acyclics would be low by the per cent of diolefins and unsaturated naphthenes. Diolefin contents were generally found to be very low. An indication of the branchiness of the paraffins and olefins is afforded by analyses of low boiling fractions in which naphthenes contents are negligible-for example, in the C d , Ca, and Ce fractions. Yields and olefin contents of C4 and CSfractions are presented in Table V, and compositions of narrow-boiling CSfractions are illustrated in*Figures1 and 2. High olefin contents occurred in fractions from gasolines produced a t high cracking temperatures with moderate conversions (samples 2 and 4). Ratios of isobutylene to normal butenes for the samples described in this article are on the order of 0.4/1 t o 0.5/1, or very close to the equilibrium values calculated from thermodynamic data (8). A large number of light hydrocarbon analyses show values ranging from 0.4/1 to 0.7/1 for operations a t the same temperature levels. Ratios of isobutane to n-butane are, on the other hand, very high, ranging from 4/1 t o 8/1. Such ratios are far above the calculated value of 0.5/1. An explanation of the differences between the iso-to-normal ratios for the paraffins and olefins is afforded by Greensfelder and Voge (6). They deduce from their studies on the catalytic cracking of pure hydrocarbons that, under suitable reaction conditions, the chain-branching isomerization of normal olefins, followed by saturation by hydrogen transfer, leads to the production of isoparaffins. c6 fractions are comparable in olefin content to the corresponding C4fractions, as shown in Table V.
TABLE1'. COMPOSITIONS O F Ca AND (26 FRACTIONS FROM PARAFFINIC FEEDSTOCKS Sample No. C4 fraction Yield on feed, vol. % Butenes, vol. Iso-C4Ha,n-C4%a Actual Theoretical equil. 160-CaHio/n-CaHio
199
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1947
1 10.8 29
2
3
23.6 50
27.4 30
4 20.7 44
5 15.9 32
0.35 0.67
0.41 0.59
0.46 0.59
0.39 0.59
0.43 0.59
.. ..
..
* *
..* .
4.00 0.45
8.09 0.45
12.8 47
13.4 31
9.2
30
14.8 48
5.8 31
The data plotted in Figure 1 show that the olefin peaks occur regularly a t certain boiling points which characterize particular olefins or groups of olefins. For example, the peak at 100-103' F. is due to trimethylethylene, a t 153-158" F. to hexenes, a t 203209" F. to heptenes, a t 241-251" F. to octenes, and a t 297301 O F. to nonenes. Conversely, broad valleys occur in the olefin curves in the 130-150' F. boiling range; these reflect the presence of sizable proportions of 2-methylpentane and 3-methylpentane. The valleys in the 80-90" F. boiling range are due to isopentane. %-Hexane and the higher normal paraffins are present only in small proportions, if a t all. This conclusion was confirmed by octane number determinations on narrow-boiling fractions. NAPHTHAS FROM NAPHTHENIC FEED STOCKS
The last four of the nine samples listed in Table I were obtained by the Fluid Catalyst cracking of three essentially naphthenictype feed stocks C, D, and E , representing intermediate, high, and low boiling ranges, respectively. Silica-alumina synthetic catalyst was employed in the production of all four naphtha samples. The aviation gasolines from the samples employed for these composition studies had octane numbers ranging from 87 to 96 by
the A.S.T.M. Aviation method, when containing 4.0 cc. of tetraethyllead per gallon. Samples 6 and 7 were produced a t 975 ' F. with moderate and high cracking severities, respectively, from feed C (light Coastal gas oil) which distilled between 420 O and 628' F.; feed C shows, by analysis, a content of 35 weight yo naphthene rings and 12 weight yo aromatic rings. Sample 8 was produced a t 975" F. from feed D (heavy Coastal gas oil) boiling between 495' and 958 O F. and containing 33 weight % naphthene rings and 12 weight 70 aromatic rir;gs. High boiling feed D is more easily cracked than feed C, and, despite equal conversions of feed at the same cracking temperature, sample 8 was actually produced a t less severe cracking conditions than was sample 6.
=.r: U U
1
I
I
I
I
I
I
I
1
1 250
I
I
I
100
t
+
f 4
>
90
; 2 I 100
I50
200
300
M I D - B O I L I N G POIN7,OF.
Figure 3. OctaneNumber Trend with Boiling Point for Cracked Naphthas from Paraffinic Feeds (A)
Sample 2: Tinsley gas oil feed, 975'F., 65% conversion gas oil feed, 975'F., 80% conversion
(B) Sample 3: Tinslay
The last fuel (sample 9) was produced at 750 O F. from feed E (Mirando kerosene), which distills between 382 O and 552 F. and contains 48 weight yo naphthene rings and 13 weight % aromatic rings. FRACTIONS OF AVIATION GASOLINE BOILINGRANGE.Table VI lists yields of fractions in the aviation gasoline boiling range of the naphthas from the naphthenic feeds, along with the composition of these fractions. Composition data for these naphthas are given graphically in Figure 4. Data are presented in Table VI and Figure 4 to show that sample 6 is moderately olefinic with the olefins concentrated in the lower boiling fractions. Relatively high naphthene and aromatic contents are also observed. Sample 7, which is comparable to sample 6 except that it was produced with greater cracking severity, has less olefins and naphthenes and considerably more aromatics. The 200-350" F. boiling range fraction of sample 7 includes many narrow cuts containing greater than 90 volume % aromatics. In contrast to the products obtained from medium boiling range feed C, sample 8 derived from high boiling Teed D shows a high olefin content. Further, the olefin content increases in the higher boiling fractions, and the olefin contents far exceed the amounts of acyclics present; this indicates that the naphthenes are mostly unsaturated. Aromatics concentrations are relatively low. Aviation gasoline from sample 8 has an A.S.T.M. Aviation octane number with 4.0 cc. of tetraethyllead of 87.0 as compared with 91.1 and 95.5 for samples 6 and 7, respectively; this illustrates the desirability of high aromatic hydrocarbon content and low olefin content in aviation fuel. Supercharged rich rmxture octane numbers also are greatly influenced by aromatic hydrocarbon concentrations, the higher concentrations being the most desirable. Sample 9 is notable for general good quality in having a low olefin content together with relatively high naphthene and aromatic hydrocarbon content; it yields an aviation gasoline having an
INDUSTRIAL AND ENGINEERING CHEMISTRY
200
SAMPLE NO. 6
IO0
t-
SAMPLE
FEED: LIGHT COASTAL GAS O I L T E M P E R A T U R E , OF.: 975 C 0 N VE R S I 0 N .V 0L.70 : 65
FEED: T E M P E R A T U RE.OE:
Vol. 39, No. 2
NO. 7
L I G H T COASTAL G A S O I L
074
0o
Z
w
v U
W
a w
60
H 2
J
0
:: $ 40 -
t v)
0
a
0"
20
c)
0
20
40
80
60
100 0
VOLUME PERCENT
20
IOC
t-
60
80
IO0
SAMPLE NO. 9
SAMPLE NO. E FEED: T E M PE R A T U RE,O F: : CON V E R S I ON, V O L .To:
40
DlSTl LLED
H E A V Y COASTAL GAS O I L 975
FEED: T E M P E R A T U RE.OE: CONVERSION,$OL.
65
MI RANDO KEROSENE 750
2.60
380
80
Z W
u a
w
w
PL W
I
0
300 +"
60
I
9
0
J
Q
0
::
5-
0 220
40
0
t
m
v)
:z: 0
f
-
140
20
U
0
60 20
40
60
00
100 0
20
40
60
VOLUME PERCENT DISTILLED
Figure 4. Compositions o f Naphthas Produced from Yaphthenic Feed Stocks b y Cracking with Fluid Silica-Alumina Catalyst
80
0
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1947
201
illustrates, the concentrations of benzene in the fractions anaCOMPOSITIONS OF NAPHTHAS FROM NAPHTHENIC lyzed are low. FEEDSTOCKS With the same catalyst and under comparable cracking condiSample No. 6 7 8 9 tions toluene yields from the naphthenic naphthas are higher than Sample boiling a t 116-200° F. those from the naphthas obtained by cracking the paraffinic feed 10.0 8.5 13.1 8.6 Yield, vol. % on feed 4 Aromatics, vol. % 3 6 1 stocks; these yields range from 1.1-3.8 volume % on feed and 32 29 29 40 Napbthenes, vol. % average roughly 7 times those of benzene. Narrow fractions 65 65 70 56 Acyclics, vol. yo 34 20 68 6 Olefins, vol. % contain as high as 88 volume % toluene (Figure 4). Yields of xylenes plus ethylbenzene amount to 2.6-6.9 volume 6 . 5 6 . 4 7 . 5 5.6 30 60 14 44 yoon feed. These yields are roughly in a 2/1 ratio to comparable 62 26 45 36 toluene yields, the same ratio as found for the paraffinic feed 18 15 41 21 8 11 73 28 stocks. The yields of C8 aromatics from the naphthenio feed Sample boiling at 25C-300° F. stocks are, in general, considerably greater than the yields from 6.7 7.4 6.7 7.5 Yield, vol. % on feed 65 93 83 34 Aromatics. vol. % ' the paraffiic feed stocks. The data plotted in Figure 4 show 38 40 1 10 Naphthenes, vel:"% that narrow fractions may contain as high as 98 volume % Ca 7 6 26 7 Acychcs, vol. % 6 2 65 11 Olefins, vol. % aromatics. The high concentration of C8 aromatics in the aviation gasolines from light Coastal gas oil feed stock, with attendTOLUENE, AND CSAROMATICS TABLE VII. YIELDSOF BENZENE, ant absence of the normally low octane number Ca acyclics and FROM NAPHTHENIC FEEDSTOCKS naphthenes, would contribute to a high, supercharged, rich octane Sample KO. 6 7 8 9 number.
TABLEVI.
Total
8.23
U.bU
U.15
3.79 6.93 11.22
1.07 2.58
-
3.80
1.66 3.70 6.74
A.S.T.M. Aviation octane number of 95.8 with 4.0 cc. of tetraethyllead per gallon. With few olefins to be saturated, there would be little gain in octane rating from the hydrogenation of this naphtha. Figure 5 shows the trends of A.S.T.M. Aviation octane numbers with boiling range for samples 6 and 8. The fractions for octane number determinations were distilled through columns of twenty-five plates and show effects of only the more important composition changes. I n both samples the octane number improves with increasing boiling point above 200 F. In the higher boiling range sample 6 has fractions which reach 100 A.S.T.M. Aviation octane number plus 4 cc. of tetraethyllead per gallon. This is attributed to the high content of aromatics, 83 volume yoin the 250-300 F. fraction,and to the low olefin content. In contrast, sample 8 shows but a small gain in octane number for the higher boiling fractions, with the best cuts reaching only 91 A.S.T.M. Aviation octane number plus 4 cc. of tetraethyllead per gallon. For sample 8 the aromatic hydrocarbon content is low and the degree of unsaturation is high (Table VI). The data of Table I shorn that sample 8 has the lowest A.S.T.M. Aviation octane number of all the samples for which data are given in this article; this is in line with the composition data: AROMATICS. Yields of benzene, toluene, and C8 aromatics (xylenes and ethylbenzene) produced from the naphthenic feed stocks C and E in samples 6, 7, and 9 (Table VII) are, for comparable cracking conditions with the same. catalyst, higher than those obtained with the paraffinic-type feed stocks. Again a tendency is exhibited for increased aromatics yield with increasing cracking severity and lower boiling feed stocks. Even though it was cracked a t the relatively low temperature of 750 O F., the product from feed E (Mirando kerosene containing 61 weight Yo rings) showed a relatively high yield of aromatics. Yields of benzene, toluene, and Csaromatics in the case of sample 8, which was derived from high boiling feed D (heavy Coastal gas oil) are definitely lower than the corresponding yields obtained from paraffinic feed A (Tinsley gas oil) a t the same cracking temperature and conversion. These low aromatics yields are no doubt due t o the relatively mild cracking conditions actually employed in cracking feed D to moderate conversion a t 975" F. Aromatics yields and concentrations in fractions from sample 8 are notably improved above 300"F. (Figure 4). Benzene yields frov the naphthenic feed stocks are low, amounting to only 0.15 to 0.50 volume % on feed. As Figure 4
TABLE VIII.
YIELDS OF NAPHTHENES" FROM NAPHTHEXIC FHED
STOCKS
Sample No. Yield, v 01. % on feed Cyclopentane IvIetbylcyclopentane cyclohexane Dimethylcyclopentenes Methylcyclohexane ethylcyclopentane Total 0 Includes any cyclo-olefins present.
+
+
6 . .
0.8
1.9 1.1 1.3 4.6
7
8
9
0.2 1.6 0.7 Q 3.6.
0.6 2.5 1.7
0.1 2.1 1.7 1 2
6.4
K.6
Analysis of the c8 aromatics contained in samples 6, 7, and 8 was made by the Petroleum Refining Laboratory of the Pennsylvania State College with Raman spectra measurements (4). The analyses showed that, within the limit of error of the determination, the proportion of ethylbenzene in the CSaromatics was the same for each of the three samples (9 to 13 volume yoon the total Ca aromatics). Also the proportions of p-xylene (15 t o 22y0),mxylene (43-48%), and o-xylene (2032%) were not appreciably different in the three samples. The Cg aromatics from a naphtha comparable to sample 3 have approximately the same distribution of the four C8 aromatics. Equilibrium data obtained a t the National Bureau of Standards ( l a ) show that a t 975" F. the ethylbenzene concentration in CSaromatics is 14 volume %, the p-xylene concentration is 20 volume yo,the m-xylene 42 volume yo,and the o-xylene 24 volume yo. These values agree reasonably well with the analyses obtained on the Fluid Catalyst-cracked CS aromatics.
I50
200 250 M I D - B O I L I N G POINT, OF.
300
5C
Figure 5. Octane Number Trend with Boiling Point for Cracked Naphthas from Naphthenic Feeds (A)
(B)
Sample 6: light Coastal gas oil feed, 915' F., 65% conversion Sample 8: heavy Coastal gas oil feed, 975' F.. 65% conversion
202
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
NAPHTHESEB.As in the case of the products from paraffinic feed stocks, the iiaphthene content's of the naphthas from naphthenic-type feed stocks are higher at conditions of low cracking severity and higher boiling feed stocks from a given type of feed. Very high concentrations of naphthenes in the fractions of aviation gasoline boiling range are obtained by low temperature cracking of Mirando kerosene, a feed that has 61 weight Vorings. The olefin contents of the fractions boiling higher than 200" F. in the naphtha from heavy Coastal gas oil feed stock are greater than the content of acyclics; this indicates the presence of unsatxrated naphthenes (cyclo-olefins). Table VI11 furnishes yield data for the main naphthene hydrocarbons identified in the cracked samples obt'ained from naphthenic feed stocks. Cycloparaffin yields necessarily include the corresponding cyclo-olefins. Cyclopentane yields are lorn, as was the case vitli the paraffiiic feed stocks; they range from 0.1-0.5 volume % on feed. The data of Figure 4 shorn that the highest concentration of cyclopentane measured in a narrow fraction is 28 volume % (sample 8). Yields or' ~~~~~~~~~~clopentane plus cyclohexane are about twice as great as those obtained from t'he paraffinic feed stocks; they range from 1.6-2.5 volume 70on feed. Narrow fractions from all of the naphthas studied have relatively high concentrations of naphthenes, on the order of 70 volume %, in the 150" to 180" F. boiling range (Figure 4). TABI E IX. COMPOSITIONS OF Cd AND Cs F R u m o N s SAPHTHCXIC FEED STOCKS Saniple S o . C I fraction Yield on feed, vol. R Butenes, 701. 5% Iso-C
