PRODUCT AND PROCESS DEVELOPMENT out a t temperatures ranging from 85" to 210" C., with air and with organic peroxides. The products in general were unsatisfactory plasticizers. Polymers of the n-propyl ester were the best of this group, but were less efficient than the di-n-butyl itaconate polymers. Since the completion of this research, several reports have described attempts to prepare plasticizers by addition polymerization. Among the monomers employed were various acrylates (1,8, IO), as well as vinyl acetate, allyl acetate, and allyl chloride (1); in all of these studies, chain transfer agents were used to limit molecular weight. I n the writers' experience, many of these monomers, polymerized without added chain transfer agents, produce incompatible or ineffective plasticizers, undoubtedly owing to the high molecular weights of the products.
microanalytical and infrared determinations; and to W. M. McLamore for valued suggestions. literature cited
Ali, M. D., Mark, H. F., and Mesrobian, R. B., IND. ENG. CHEM.,42, 484-8 (1950). Anschtltz, R., and Reuter, F., Ann., 254, 129-49 (1889). Clash, R. F., Jr., and Berg, R. M., IND.ENO.CHEM.,34, 1218 (1942).
D'Alelio, G.F. (to General Electric Co.), U. S. Patent 2,297,290 (Sept. 29, 1942); 2,340,108(Jan. 25, 1944). Hochstein, F. A,, J. Am. Chem. SOC.,71, 305-7 (1949). Kane, J. H., Finlay, A. C., and Amann, P. F. (to Chas. Pfizer & Co.), U. S. Patent 2,385,283 (Sept. 18, 1945). Lawson, W. E. (to E. I. du Pont de Nemours & Co.), Ibid., 2,062,917 (Dec. 1, 1936). Leonard, F., Szlachtun, A. J., and Cort, I., J. Polurner Sci., 11, 539-44 (1953).
Acknowledgment
Paytash, P. L.,and others, J . Am. Chem. SOC.,72, 1415-16
The investigation here described was conducted under a fellowship sponsored by Chas. Pfizer & Co., Inc. The authors are also indebted to W. A. Woodcock, Carbide and Carbon Chemicals Corp., and Paul Sharpe, Socony-Vacuum Oil Co., who furnished some of the physical testing; to A. J. Frankel, J. W. Herrmann, P. C. Horsting, and W. J. Murphy, who prepared some of the compounds; to G. B. Hess, J. R. Means, and associates for
(1950); 74, 4549-52 (1952); 76, 3500-1 (1954).
Rehberg, C. E.,and Siciliano, J., IND.ENC.CHEM.,44, 2864-6 (1952).
Roberts, E.J., Ambler, J. A., and Curl, A. L. (to Secretary of Agriculture), U.S. Patent 2,448,831 (Sept. 7,1948). RECEIVED for review March 25, 1954. ACCEPTED February 24, 1955. Presented in part before the Metropolitan Long Island Subsection of the -4MERICAN CHEMICAL SOCIETY, 1951.
Recovery of Catalytic Cracking Stock by Solvent Fractionation PAUL H. JOHNSON, K. L. MILLS, JR., Research Division, Phillips Petroleum
0
AND
Co., Bartlesvifle,
B. C. BENEDICT Okla.
N E product common to almost all petroleum refining is the residuum. For every barrel of distillate produced, refiners are committed to sell or use a proportionate amount of this residue. The yield of such materials depends upon the crude source. Normally, these residues are blended with lighter oils for sale as low profit liquid fuels. Some residuals have found a ready market as high profit road and building materials, but such outlets can absorb only a small fraction of the potential supply * I n recent years the demand for residual fuels has not kept pace with the increase in crude runs. On the other hand, the lighter oils have been in increasing demand as distillate fuels and for processing into other products. These factors, coupled with the generally low price offered for residual fuels, have made the practice of blending petroleum residues to fuel oil specifications highly unattractive. Most asphalts and residual fuels are potential sources of additional catalytic cracking stock. The amount may be as much as 50 to 75%. These heavy oils are capable of producing high octane gasoline in yields equal to those from lighter stocks. The employment of deep vacuum flashing t o recover additional cracking stock can cut the residuum yield by many barrels. Other processes such as visbreaking and coking can likewise be employed t o accomplish the same purpose. As these processes are applied in an effort to get deeper into the crude, certain components that have an adverse effect on catalytic cracking are included in the recovered oils. The progressively heavier petroleum fractions contain progressively larger amounts of materials deleterious to the cracking opera-
1578
tion. Thus, the potential cracking stocks of most residues contain relatively large amounts of metal compounds, polynuclear aromatics, resins, and sulfur and nitrogen compounds. Metals, which have received a great deal of attention, differ from most deleterious materials in that they are accumulated on the catalyst. Continued feeding of even trace amounts of metal compounds t o a catalytic cracker requires a continuouslv high catalyst replacement rate. Relatively large amounts of metal may preclude the operation entirely. If high-grade cracking stocks are t o be recovered from low value fuel oils, selective separation processes are mandatory. Solvent fractionation with light hydrocarbons such as propane and butane meets these requirements. While old in lube oil technology, this process has received little attention as an adjunct to catalytic cracking. light hydrocarbon fractionation process for preparation of cracking stock deserves systematic study
Extraction of petroleum residua with solvents such as propane, or butane, is an old art (1,2, 18). As a result of the work in the lube industry, light hydrocarbon fractionation became highly developed. Continuous countercurrent extraction towers of several stages are in current use. The reflux principle may be employed and excellent quality oils can be made. I n recent years the solvent process has found some application in producing cracking stocks (3, 10, l a ) . In at least one instance, cracking data on solvent-fractionated oils produced by a batch-type operation have been reported (11).
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 8
PRODUCT AND PROCESS DEVELOPMENT Judging from the literature, little systematic study has been made of the solvent fractionation process for preparing high quality cracking stock. Reconsideration of this process is dictated by recent problems relating to the over-all efficiency of the cracking operation and the best utilization of residual oils. This article describes the use of continuous countercurrent solvent fractionation for preparing premium cracking stock. It will be shown that extremely heavy oils, selectively extracted from residua, contain a minimum of unwanted materials. A comparison is made between the cracking characteristics of extracted and vacuum flashed oils. Fundamental Principles. The theories of solvent fractionation have been described (13, 16, 18); therefore, only the basic principles are outlined in this discussion. Asphaltic bitumen is a colloidal system in which the asphaltenes, because of their adsorption of resins and aromatics, are peptized. Normally liquid paraffins (pentane, hexane, etc.) partially, 01 completely, dissolve the peptizing agents and the asphaltenes coagulate. These solvents behave normally and as temperature is increased more bitumen is dissolved. The lighter, normally gaseous paraffins also tend t o behave in the same manner. However, as the molecular weight of the paraffin series decreases, the solubility of the resins and of some of the heavier and more aromatic hydrocarbons in these paraffins decreases. Thus, instead of a dry powdery precipitate of asphaltenes, a tacky material, consisting of asphaltenes, resins, and aromatics, results. As the temperature of these lighter solvents is raised from about 100" F. to the critical, the solubility of the resins and of the heavier and more aromatic hydrocarbons is further decreased. This is apparently a violation of a normal concept; however, in theory, this will occur with all solvents as the critical temperature is approached (13). From this discussion it is apparent how light hydrocarbons can be used to separate cracking stock from many undesirable materials. Besides producing an oil relatively free of high boiling aromatics, resins, and asphaltenes, the solvent process also rejects metal (nickel and vanadium), sulfur, and nitrogen compounds. The fact that metals are rejected indicates that they are associated with the resin or asphaltene fractions. Skinner (16) has shown that the majority of the vanadium in Santa Maria Valley crude is found in the propane-insoluble fraction but that a substantial amount of vanadium appears in the pentane-soluble portion. This has been verified in this laboratory by work on other crudes, and it appears that some 10 to 15% of the nickel and vanadium content of crudes is associated with volatile (but essentially propane insoluble) resins, the balance being associated with the nonvolatile asphaltenes. The volatility of these metal-bearing resins has also been demonstrated by molecular distillation studies in this laboratory. This is contrary to the conclusions of Garner and coworkers ( 4 ) . Solvent fractionation can, in general, be treated like other extraction processes. Thus, countercurrent operation and solventto-oil ratio are important in attaining the selectivity required for producing premium cracking stocks. The variables of the process are temperature, pressure, solvent-to-oil ratio, molecular weight range of the feed stock, and solvent type. Pressure and temperature are both variables because the solvent power of light hydrocarbons is approximately proportional to the density of these materials (18). Thus either temperature or pressure can be used t o control the operation. Except near the critical region, however, the effect of pressure is minor. Accordingly, pressure is normally maintained (as in this work) a t some fixed value above the bubble point of the solvent at the temperatures used. Therefore, for any given feed stock and solvent, the operating variables can be considered to be temperature and solventto-oil ratio. Higher temperatures always result in decreased yields of cracking stock. The effect of solvent-to-oil ratio on yield, however, cannot be predicted without equilibrium data. This is illustrated in Figure 1, where isobutane is used as a solvent.
August 1955
Above about 230" F., increasing the solvent-to-oil ratio decreases the residuum yield (increases the cracking stock recovery). Below this temperature the reverse is true. Figure 1 might be divided into two zones-a zone where increasing solvent-to-oil ratio gives increasing oil yields and a zone where increasing solvent-to-oil ratio produces the reverse. It should be emphasized, however, that practical operation and good selectivity can be attained in either zone. Thus, solvent-to-oil ratio is not an important variable from the yield standpoint. Almost any desired yield can be obtained by adjusting either the solvent type or the temperature. Solvent-to-oil ratio is important, however, from the standpoint of selectivity. I n general, to a solvent-tooil ratio of about 15 : 1, increasing the solvent-to-oil ratio results in increasingly better quality oils.
w
10
n
3
a V
n
g
225' E 205'
F.
Y
= 4
= I
2
Figure 1 .
I 4
-
I
I
I
I
6
0
10
12
SOLVENT TO OIL RATIO
Effect of solvent-to-oil ratio on yield of cracking stock West Kansas 15% reduced crude Solvent, isobutane Pressure, 500 Ib./sq. inch
Pilot scale solvent fractionation unit i s used with representative reduced crudes as feed stocks
The pilot solvent fractionation unit consists of a 25-foot column, 3 inches in diameter, with the necessary charge pumps and control instruments. A diagram of the assembly of the apparatus is shown in Figure 2. For contacting of the phases the column has staggered horizontal baffles spaced 2 inches apart. Each baffle covers 50% of the cross-sectional area. A charge rate of 14 gallons per hour of solvent and 2 gallons per hour of oil has been maintained without flooding. The temperatures in the column are maintained by electrical heaters wrapped on the outside of the column. The bottom of the column is immersed in a heated glycol bath to reduce heat losses. A temperature controller is used to regulate the temperatures of the solvent and oil feed as well as the glycol bath, Other temperatures are manually controlled to &lo F. The pressure on the column is held constant with a pressure controller. The interface level is maintained in the lower portion of the column with a liquidlevel controller. This apparatus has been used to fractionate a wide variety of materials. By a method described previously ( I d ) , the apparatus has been rated to have 3.5 to 4 theoretical stages when using a combined oil and solvent rate of 12 t o 16 gallons per
INDUSTRIAL AND ENG INEERING CHEMISTRY
1579
PRODUCT AND PROCESS DEVELOPMENT I
- - - - - .__. - - - - - __- -
SOLVENT CONDENSER
+$-
-m
TO SEWER
-VENT
?----I
I
I
COOLING WATER
N In
K
h
SOLVENT
COLUMN BAFFLES
COVER 50 % OF CROSS SECTION AREA, BAFFLES STAGGERED 2"
APART I
f
3
8
t
t?
I
0
4
0
54
lL
~
VEkT
I
VENT-
'
I5al
$2 vir
ELECTRIC HEATER
E-2 PULSAFEEDER VARIABLE
p"
t -r
"
0-12GPH STR\CPEO RESIDUUM
Figure 2.
Pilot plant solvent fractionation unit
hour. This range of rates was used throughout the work reported in this article. Feed Stocks. The reduced crudes were obtained from a Western Kansas crude and a West Texas-Panhandle crude and represent extremes in mid-continent types. Such extremes aerve to illustrate the utility of the solvent fractionation process. The Kansas crude is a paraffin-naphthene base crude containing approximately 13% of 100-penetration asphalt. The West Texas-Panhandle crude is essentially a paraffinic base crude containing less than 474 of 100-penetration asphalt. Inspection data for the several reduced ;rude samples are given in Table I.
Table 1.
Properties of Reduced Crudes PanhandleWestern West Texas Kansas Per Cent of Crude 10 8.5 24 15
40 50 Gravity OAPI Carbon kesidue (Ramsbottom), wt. % Sulfur, Nt. % Metals, p.p.m.
NiO
VeOs Viscosity (210° F..), S.U.S.6 Softening point (ring and ball), 0 F. Penetration ( 7 7 O F., 100 g., 5 see.) Pentane insoluble, wt. % ' Unpublished method, Phillips b Not attainable. C Saybolt Universal seconds.
1580
.. .. 16.7 8.61
0.74
966 1008
16.2 11.4 0.81
15.9 3.44 1.05
.... .. 10.3 7.5 1.31
23.2 28 9 700
1360
35 139 384
soft
soft
soft
102.5
Soft
soft
soft
213 16.6
2.74
27.0
40.0
3.30
Petroleum Co.
9.48
68 220 8200
Choice of solvent is dictated by light oil content of residuum
Effact of Feed Type. A long and a short reduced crude produced commercially from each of two different crudes were used as a feed to the solvent fractionation. A long reduced crude is produced by atmospheric distillation or a combination of atmospheric and mild vacuum reduction. A short reduced crude is the residual product of deep vacuum flashing. For a given temperature and solvent-to-oil ratio, it is possible to recover more oil from a long residuum than a short one, but with some sacrifice in selectivity, This effect of feed type on yield is illustrated in the graph of Figure 3. (The total height of the bars of this graph and Figures 4 and 5 represents the reduced crude feed to the solvent process in terms of percentage of total crude. The yields of residuum and oil from each reduced crude feed are indicated by the division in the bar.) For example, a Western Kansas 24% reduced crude was further reduced to 7.1 % crude bottoms with propane at a 6: 1 solvent-to-oil ratio and a temperature of 175" F. However, a t the same operating conditions, a 15y0 reduced crude from the same source could be reduced to only 11,270 bottoms. Similar results were obtained with a 10 and an 8.5% reduced crude from West Texas-Panhandle crude and are also shown in Figure 3. I n this case, with a 6: 1 piopane-to-oil ratio and a temperature of 125" F., the 10% reduced crude yielded 3% residuum. The 8.5y0reduced crude yielded 5.5% of crude as a bottoms product. The data show that, as the result of the light oil loading of the solvent, less material is rejected when a long reduced crude is charged. The use of a long reduced crude as feed stock permits deeper extraction of the crude a t a selected set of conditions and with a given solvent. However, for a fixed refinery crude charge, the long reduced crude will require a larger unit than will a short reduced crude, and, as will be shown, the use of a long reduced crude as a feed stock results in loss of selectivity. On the other
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 8
PRODUCT AND PROCESS DEVELOPMENT hand, the solvent fractionation of a short reduced crude using a particular solvent may limit depth of crude reduction as Figure 3 illustrates. This c8n be overrome by selection of an appropriate hydiocarbon solvent. 25 Effect of Solvent Type. The solvent power of 20 1ig h t hydrocarbons i n c r e a s e s I5 with i n c r e a s e d inolecular weight The solvent x p o w e r of t h e s e solvents also de-
9"
pends on the light 5 oil loading of the solvent ph ase. Thus, as the 0 WEST KANSAS PANHANDLE- W TEXAS topped crude i E REDUCED CRUDE REDUCED CRUDE f u r t h e r reduced 175'F,,6/1 PROPANE 125'F 611 PROPANE TO OIL RATIO ~ $ 0 1RATIO ~ prior to the sol5 5 0 FSIG. 450 PSIG. vent fractionation step, lower temFigure 3. Effect of feed type on yield of cracking stock pere tures and/or higher molecular weight solvents must be used in order to recover maximum gas oil. As shown in Figure 4, propane at 175" F. fails to reduce t h e 15y0 residuum t o as low a value as the 24% residuum a t the same temperature. Lowering the temperature to 136" F still does not reduce the short reduced crude to the degree obtained with the long reduced crude. When the lowest practical temperature is reached it is necessaiy to use a more potent solvent. As shown in Figure 5, only 70% of PanhandleWest Texas 10% reduced crude was recovered as cracking stock with propane a t 125' F. By switching to isobutane, 8201, of the reduced crude was recovered as a clean gas oil at 225' F. The effect of higher temperatures with isobutane is also shown in Figure 5 . For even shorter reduced crudes, n-butane or pentane may be the practical solvent. Accordingly, by judicious choice of solvmts one may operate in a practical range of solvent-to-oil ratios, temperatures, and pressures with almost any residuum. Typical yield curves showing the effect of solvent-to-oil ratio as well as solvent type and temperature are shown in Figures 1 and 6. Solvent fractionation i s considerably more selective than vacuum flashing
Propane or isobutane selectively rejects aromatics in preference to paraffins and naphthenes. Also, the higher molecular weight components are rejected in preference to the lower molecular weight materials. One would therefore expect solvent-fractionated oils to be less aromatic and to contain less undesirable constituents than corresponding vacuum-flashed gas oils. The factors affecting selectivity in solvent fractionation are solvent-to-oil ratio, solvent type, and the proportion of lighter oils associated with the charge. The effect of the first two factors can be judged from the physical properties of the fractions produced. The effect of the latter factor is difficult to show, inasmuch as the products to be compared represent different percentages of the crude. This difficulty can be overcome by indirectly comparing the solvent separated fractions with corresponding fractions of the crude prepared by vacuum flashing. For example, vacuum-flashed and solvent-fractionated oils from a short reduced crude were compared with similarly prepared fractions from a long reduced crude. The results show that changing from a long to a short reduced crude effects a marked improvement in the selectivity of the solvent process.
August 1955
Cracking stocks prepared by vacuum flashing have been used in these investigations as a basis for comparison with solventfractionated oils. The vacuum gas oils were prepared in a laboratory flash unit described in a previous article (6). Rejection of Metals. One of the criteria used in evaluating a catalytic cracking stock is its metal content. It is well known that iron, nickel, and vanadium are highly deleterious to cracking catalysts. Other metals, such as copper (7), sodium, and potassium, are also undesirable. These metals for the most part find their way to the catalyst via entrainment during vacuum flashing ( 5 ) . However, a significant amount of metals may be volatile in nature. Thus, deep vacuum flashing is almost certain to produce metal-contaminated cracking stocks a t some stage of reduction, either by entrainment or volatilization, or a combination of the two. A long reduced crude (24% Western Kansas residuum) was both propane fractionated and vacuum flashed. I n several operations progressively deeper oil cuts were made. These oils were analyzed for nickel and vanadium and the data plotted as a function of percentage residuum as shown in Figure 7. The selectivity is very sensitive to solvent-to-oil ratio. At solvent-To-oil ratios below 4.6: 1, the solvent process is an improvement over vacuum flashing only a t deep reSOLVENT- FREE ductions. At solvent-to-oil OVERHEAD ratios of 6: 1 and higher, 20
n ~ ~ ) ~ the ~ solvent ~ ~process - ~pro&C duces a cleaner oil than
w
n
u
I5
s
x
9
d o e s v a c u u m flashing. These data are typical of those from a long reduced crude. I n a similar experiment
10
a short reduced crude (Western Kansas 15% 5 residuum) was solvent fractionated and vacuum flashed, I s o b u t a n e w a s 0 used as the solvent instead TEMP'F 175 175 135 of p r o p a n e . F i g u r e 8 64 PROPANE TO OIL RATIO shows t h a t t h e "Ivent WEST KANSAS REDUCED CRUDE PRESSURE-550 PSIG. process i s c o n s i d e r a b l y Figure 4. Effect of feed better than flashing in retype and temperature on j e c t i n g metals, even a t solvent-to-oil ratios as low yield of cracking stock as 3 : l . Thus, with short reduced crudes the selectivity of the solvent process is improved and high solvent-to-oil ratios are not required. The solvent process is also effective in removing metals from paraffinic base crudes low in metal content. Typical data are shown in Figure 9 for a Panhandle-West Texas crude residuum. Compared with vacuum flashing, a 70% average reduction in metals was accomplished with ease a t 7 . 5 :1 isobutane-to-oil ratio. Some propane data are also shown in Figure 9, demonstrating the relative selectivity of the two solvents. On the basis of these and other data it is concluded that propane is slightly more selective than isobutane. The selectivity of the solvent process is limited as deeper cuts are made into the crude. At some point representing a small percentage of crude residuum, the solvent process can have no advantage over vacuum flashing. At this juncture the solventfractionated oils approach the character of vacuum oils. However, it may be impractical to reach this degree of reduction by vacuum so that, throughout the practical operating range of the vacuum flash process, solvent fractionation will produce cleaner gas oils. Rejection of Carbon Residue Forming Materials. The carbon residue (ASTM Method D 524-52T) of a cracking stock appears
INDUSTRIAL AND ENGINEERING CHEMISTRY
1581
PRODUCT AND PROCESS DEVELOPMENT SOLVENT -FREE OVERHEAD PRODUCT
12
FREE 0SOLVENTRESIDUUM PRODUCT
\
7-
:I
w
2 6V
L 0
w
ISOBUTANE 265'F:
6 5 2 5> Ia
g 4-
ISOBUTANE
w
a a
TEMP'F.
125
265
250
225
611 SOLVENT TO O I L RATIO PANHANDLE- W. TEXAS REDUCED CRUDE PRESSURE: 500 PS1.G. EXCEPT PROPANE, 450 P S l t
250' F:
1
PROPbNE 125 F. ISOBUTANE
34
-
I
I
I
I
I
Temperature (av.) O F. Space rate, wt. o i oil/(hr.) (wt. of catalY st ) Pressure, lb./sq. inch gage Steam diluent, lb./bbl. of oil Processing period, min. Carbon on catalyst mean value), a t % Catalyst activity (P illips activity index,
6
Catalyst activity (Jersey D prox.) Type of catalyst
+
L, ap-
I
1
2
3
I
I
t
a
4 5 6 RESIDUUM, VOL. % OF CRUDE
0
Figure 13. Viscosity-gravity constants of gas oils from Panhandle-West Texas 10% reduced crude
I
characteristics of the feed in question, so that all feed stocks were cracked with a catalyst having essentially the same average (mean value) carbon deposit. This method of evaluating cracking stocks measures the characteristics of the oil but does not measure the accumulative effect of trace metals that would result from an equilibrium operation in a commercial plant. The effects of metal contamination, however, can be estimated for any particular case if the metal content of the oil is known. Experience has shown that approximately 9570 of the metals in the oil are'retained on the catalyst. Typical operating conditions used on the heavy types of oils were as follows: 900 1 to 4 10 15 5 t o 70 1.5
100
29 Plant equilibrium montmorillonite
Cracking Results. Results of cracking the solvent-fractionated and vacuum-flashed oils from the two reduced crudes arc shown in Table 111at 5iy0conversion. These data demonmate very well the superiority of the solvent-fractionated oils. For example, in the case of the Panhandle oils, the solvent-fractionat,ed stock produced 54y0 less carbon than the vacuum-flashed stock; in the case of the Western Kansas oils, the carbon reduction was 34%. The smaller reduction in carbon in this latter case is believed to be the result of the more complex nature of the Western Kansas oils, which lessens the chance for the solvent to exhibit selectivity. Carbon deposition data obtained over a range of conversion levels are shown in Figure 15. The improvement in gasoline yield, although small percentagewise compared with the reductions in carbon, is well worth considering. The advantage of the solvent-fractionated oils over the vacuum-flashed oils is of the order of 5 to 7y0 additional gasoline. The low yield from the vacuum oils emphasizes the poor selectivity of this type of feed stock separation. Such oils contain traces of asphaltenes and relatively large percentages of resins and polynuclear materials which produce very little gaso-
1584
iI
SOLVENT SEPARATION 500 PSlG
5 5-
e',
I
PROPANE 6 TO l2.7/1, 450 PSlG ISOBUTANE - 500 PSlG
line when catalytically cracked. I n addition, the solvent-fractionated oils tend t o produce more light olefins. These differences are not large but are important, when such adjunct processes as catalytic polymerization and alkylation are considered. The method of feed stock separation appeared to have little effect on octane number. The cycle stocks produced from the vacuum-flashed oils, however, were somewhat more aromatic than those from the solvent-fractionated oils. The heavy oils used in this cracking evaluation would normally represent 8 to 10% of the fresh feed to a cracking unit. For the purpose of illustration, it is assumed that a nominal 40,000 barrel per day unit having a coke burning capacity of 28,000 pounds per hour is available. Substitution of solvent-fractionated oil, barrel-for-barrel, for vacuum-flashed oil, would result in a substantial reduction in coke yield. Thus, nearly 5000 barrels per day more fresh feed could be processed, resulting in an increase of 2200 barrels per day of catalytic gasoline. I n addition, if it is assumed that alkylation is also available, over 760 barrels per day of additional alkylate could be made from the increased yield of olefins, bringing the total increase in gasoline to nearly 3000 barrels per day. If the improvement in metal contarnina-
Table II.
Properties of Stocks Prepared for Catalytic Cracking Evaluation PanhandleWestern West Texas Kansas Cracking Stock Preparation Method Solvent Vacuum Solvent Vacuum
Reduced crude, vol. yo of crude Cracking stock, vol. % of crude Vacuum distillation", F. at 760 mm. Condensed, % 5
in ~~
15 20 30 Gravity OA.PI Carbon 'residue (Ramsbottom) wt. % Sulfur 'wt. % NitroLen wt. % Moleculir weight ;\letals, p.p.m. NiO
VZOS
7.0
7.0
15.4
15.4
3.8
3.7
7.8
7.9
975
1020 . ~
908
~ 992 ... ~
964 985 .~~
934 972
....
.... . ,. .
23.2
20.5
1.88 0.56 0.20 784
4.58 0.78 0.30 699
2.31 0.79 0.23 709
4.23 0.92 0.34 663
1.1 0.5
7.1 5.3
0.9 2.8 252 0.844 16.5
14.8 287 0.863 22.8
1035 1041
1012
247 Viscosity, (210O F,), S.U.S. b 239 0.826 0.846 Viscosity-gravity constant 19.4 Carbon in aromatic rings, % 10.1 a Unpublished method, Phillips Petroleum Co. b Saybolt Universal seconds. C n-d-M ring analysia (9).
INDUSTRIAL AND ENGINEERING CHEMISTRY
ioii'.
1034 20.8
ioii' '
1037 18.2
2.8
Vol. 47, No. 8
PROQUCT AND PROCESS DEVELOPMENT I
I
‘It I
15 a
SOLVENT SEPARATION-500PSlG
Y w
VACUUM V 4
SOLVENT SEPARATION-500 PSlG
0.01
2
4
8 IO 12 RESIDUUM, VOL I OF CRUDE
6
14
16
Figure 14. Sulfur and nitrogen content of gas oils from West Kansas 15% reduced crude
tion due t o the use of the more selective separation process is considered, even more additional cmcking capacity would be realized. The solvent fractionation process produces high quality asphalts
If a profitable asphalt market is available, it is usually desirable t o reduce a portion of the crude to the “specification” asphalt stage. This can be done by either vacuum flashing or solvent fractionation. The cracking stocks obtained when the solvent process is used are much superior, as has been demonstrated. Inasmuch as the gas oils prepared by the two processes are different, it might be expected that the aRphalt8 are also different. This bas been found to be true. These differences, in terms of asphalt “yardsticks,” are relatively minor but in general are in the direction of an improved asphalt. In this study, the emphasis has been on obtaining high yields of premium cracking stock. I n using either vacuum flashing or
Table
Ill.
Catalytic Cracking of Solvent-Fractionated and Vacuum-Flashed Oils PanhandleWestern West Texas Kansas Cracking Stock Preparation Method Solvent Vacuum Solvent Vacuum
Reduc,ed crude, vol. Cracking stock, vol.
of crude of crude
7.0 3.8
7.0 3.7
15.4 7.8
15.4 7.9
4.9 10.3
5.0 8.3
6.6 9.5
5.9 8.4
47.4 4.8 57
44.5 10.4 57
46.5 6.4 57
44.2 9.7 57
93.3 85
93.3 85
92.4 86
92.2 78
24.3 53
22.8 58
21.4 61
19.3 67
Cracked Products
Cs t o 400’ F.end point gasoline b y vol.
Research octane No. ( + 3 TEL”) Bromine No. 400’ F. and heavier cycle oil Gravity API Correlat’ion indexb a Tetraethyllead. U. 8. Bureau Mines ( 1 7 ) .
*
August 1955
h.
CONVERSION, VOL. X
Figure 15.
Carbon yield from catalytic cracking
solvent fractionation to recover maximum cracking stocks, the asphalts produced are hard, high melting materials. For example, it was possible to reduce the Western Kansas 15.4% residuum to as low as 5.58% of the crude by solvent fractionation. The resulting asphalt was a zero penetration, 290’ F. softening point material. Such a product is out of the asphalt cement range and would either have to be burned as fuel or cut back with lighter stocks. I n general, for the same yield, the solvent fractionation process produces asphalts of lower penetration and higher softening points. literature cited
Bray, U. B., and Bahlke, W. H., “Science of Petroleum,” vol. 111,p. 1955, Oxford Univ. Press, 1938. (2) Bray, U. B., Swift, C. E., and Carr, D. E., Oil Gas J . , 32, No. 24, 14 (1933). (3) Ditman, J. G., and Mertens, F. F., Petroleum Processing, 7, 1628 (1952). (4) Garner, F. H., Green, S. J. Harper, F. D., and Pegg, R. E., J. I n s t . Petroleum, 39, 278 (1953), (5) Johnson, P. H., and Mills, K. L., Jr., IND. ENC.CHEM.,44, 1624 (1952). (6) Johnson, P. H., and Stark, C. P., Ibid., 45, 849 (1953). (7) Mills. G. A.. Ibid.. 42. 182 (1950).
