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D. H. STEVENSON and HEINZ HEINEMANN Research and Development Laboratories, Houdry Process Corp., Linwood, Pa.
Residuum Hydrocracking This continuous process can operate at 3500 pounds pressure for long periods with little loss in activity, to produce Reformable gasoline
b
Gas oils resembling virgin stocks
UPGRADING
FUELS by hydrogenative processing is a relatively old art and when used with simultaneous or subsequent cracking, originally served two purposes-conversion of coal and other bituminous fuels to liquid hydrocarbons and production of large quantities of gasoline from heavier hydrocarbons. Production of hydrocarbons from coal, as developed by I. G. Farbenindustrie in Germany (7, Q), is a multistep process with a liquid phase (Sumpfphase) hydrogenation, product purification, and finally gas phase destructive hydrogenation of a middle oil from the product. This last step is similar to the hydrogenative upgrading of heavy gas oils, described in about 1930 by workers of Standard Oil Development Co. (2, 4 ) . The end product is large quantities of gasoline having a low octane number, but recent work has shown that it lends itself to upgrading by catalytic reforming ( 5 ) . After World LVar 11, some German industrial facilities for hydrogenating coal were adapted to destructive hydrogenation of petroleum residua and other heavy hydrocarbons. Preservation of the two-step, liquid phase-gas phase processing, however, makes this a complex and costly process which requires large volumes of hydrogen and operates at high pressure. Its major product is gasoline. Large requirements for heavier distillate fuels and lower investment and operating costs to produce these fuels, led to an investigation, started several years ago in the Houdry laboratories, into the possibility of converting residua to a spectrum of lower-boiling hydrocarbons by simpler means, One result of this work is the Houdresid process (3, 7) for catalytically cracking residua. Another, presented in this article, is a process for hydrocracking
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residua in one step with occasional, though infrequent, regeneration of the catalyst, and relatively low7 hydrogen requirements. Products consist of a minimum of gas and reformable gasoline, relatively large Diesel and gas oil fractions, and a recycle fraction having a Ramsbottom carbon content no higher than that of the fresh feed. Since this work was completed, another hydrogenative process for handling heavy residua has been described (6). Sufficient data are not available for a direct comparison, but the major difference between the two processes is that the Houdry process can operate for long periods of time without regeneration. In an elevated pressure process, regeneration requires depressuring, purging, regeneration, purging, and repressuring steps; therefore, it is complex, time-consuming, and costly.
Equipment and Techniques Data given here were obtained in a 2 to 4 barrels-per-day hydrocracking pilot unit designed to operate at pressures up to 5000 pounds per square inch gage. The major items of equipment are a preheater for heating the fresh feed and make-up plus recycle hydrogen to the desired reaction temperature, a series of three reactors with interstage heating or cooling jackets to control the reaction temperature, a separation system, and a recycle gas compressor, The separation system consists of a primary cooler and separator which separate liquid and gaseous products at 500' to 600' F. The secondary cooler and separator remove condensable material contained in the effluent gas from the primary separator. This two-stage separation was used to facilitate ease of operation in handling heavy materials.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Although not shown in the diagram, the secondary separator is equipped with a caustic wash system to avoid plugging the lines with ammonium polysulfide as originally occurred with high-sulfur, high-nitrogen charge stocks. A small gas bleed-off stream is taken from the recycle gas system through a pressure control valve, and its volume is kept small by adjusting the quantity of make-up hydrogen. This small gas bleed-off stream is used for analysis to show the composition of the recycle gas stream at any time. The gas flashed from the liquid product collecting tanks is measured, sampled, and analyzed. Liquid products from the primary and secondary separators are reblended in yield proportions and analyzed. Analysis of the total liquid product from the system consists of an atmospheric distillation to separate a 385O F. at 90% ASTM gasoline fraction and a total gas oil product. The total gas oil product is then distilled in a small glass column under vacuum up to the atmospheric equivalent of 1000' F. This determines the yield of residual material boiling above this temperature. C5 and heavier hydrocarbons from the gas stream flashed from the separation system are then remixed with the gasoline in yield proportions so that a representative C5+ gasoline can be tested. All yields are then calculated and reported on a diluent-free basis.
Experimental Data The most significant feature of this process is its ability to operate at 3500 pounds per square inch gage with no significant loss of catalyst activity and hence, no requirement for frequent regeneration. This is accomplished by using a hydrocarbon diluent for the residual charge stock. When charging
MAKE.UP HYOROGDl
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RECYaE
SMALL GAS 8LEEO.OFF
COhPRESSOR
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per square inch gage using 2300 standard cubic feet of recycle gas per barrel of feed. The diluent when used in the charge was 35% by volume of butane and the catalyst, 2% nickel oxide on silica-alumina. Table I1 shows charge stock inspections and Figure 1 presents product distribution data for this charge stock from stable operation. Over the entire range of operation covered, the liquid recovery was in excess of 100%. Some consumption of butanes occurred at the less severe operating conditions. Figure 2 compares product distribution obtained with butane in the charge stock, with that using no diluent, and also that using neither diluent nor catalyst. Better product distribution is shown for the operation with butane as a diluent. Hydrogen consumption is higher for hvdrocracking" with a diluent " than without, indicating better retention
RECYCLE GAS
FRESH FEED
'- - -1- --'
H E A W PROWCT I
LIGHT PROWCT
~ T O T PRODUCT L FOR A N A L Y S I S
The hydrocracking pilot plant 9
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undiluted residual feed stock, the buildup of coke in the reactor even with the most active catalyst tested (cobaltmolybdena on alumina), was such that runs could proceed no longer than 20 to 30 hours on stream before the reactor plugged. However, by adding a light hydrocarbon diluent such as 35% butane to the feed, runs of 300 hours' duration have been made with no detectable change in catalyst activity over that which occurred during the first few hours on stream. I n Table I, showing the effect of using diluents, all results are essentially initial operating results (10 to 20 hours on stream). This table shows that a substantial reduction in the amount of residual material boiling above 1000° F. occurs even without a catalyst or diluent. However, the Conradson carbon content of the 410' F.+ fraction of the product is high. In purely thermal hydrocracking, addition of a diluent makes no difference. When using a cobalt-molybdena on alumina catalyst in the absence of a diluent essentially the same reduction of residuum (boiling above 1000° F.) occuss as in thermal operation. However, the Conradson carbon content of the 410' F. + fraction of the product is considerably reduced. Operation with diluents on the other hand, shows a further reduction in residuum boiling above 1000° F. and also a further reduction of the Conradson carbon content of the 410' F. -I.fraction. There is little difference in the effect of the three diluents shown in this table. However, for ease of operation and analysis. most of the pilot plant work was carried out with iso- or n-butane as the diluent. There was no difference between the two butanes and they were used interchangeably. A large number of pilot plant runs was made with a 13% bottoms fraction of mixed South Central Texas crudes. Figures 1 through 4 representing these runs, are for operations at 3500 pounds
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15
In
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20
25
30
E"
5
0
RESIDUAL ABOYE 1000°F.,
YOLME $ OF
35
CHARBE
Figure 1. Product distribution as a function of hydrocracking depth, using both diluent and catalyst
Table I.
Effect of Additives on Hydrocracking
(15% East Texas bottoms; 3500 lb./sq. in. gage; 1.5 LHSV; 825' F. temp.: hydrogen-bottoms moleratio, 12:l;additive t o bottoms mole ratio, 1:1)
Charge Stock Yield of residual above 1000° F., wt. y o Conradson carbon of 410OF. + fraction
No Catalvst No diluent Decalin
Cobalt Molvbdate on Alumina No
diluent
Decalin
40O0-5OO0 F.
naphtha
ISObutane
70
30
33.3
31.0
27.2
23.0
22.3
10.0
11.8
11.8
5.7
3.8
4.1
4.2
VOL. 49, NO. 4
APRIL 1957
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r
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4
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Figure 2. Product distribution as a function of hydrocracking depth
1000 2
t 800 . 600
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u L
0 with quartz
z
&
Both diluent and catalyst
No diiuent; 0 with catalyst,
'100
Figure 3. Octane number and residual Conradson carbon content vs. hydrocracking depth
0 '
x 200 *"
1
0
1
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v
a *
0 Both diluent and catalyst 0 No diluent; with catalyst I 3 No diluent with quartz
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+
u: 5 0
I O
Y0 O
2
40
Y I 0 0 >
P 2 30 u > I =
e
20
av1 < Y E E
ss 70
