Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
' ~g~35 HR-1273
COAL HYD~OGENATION PROCESS
-
USI~G PETROLEUM-DERIVED SLURRYING OIL
~ACXGRo~'ND CF INVENTION
Field of Invention:
. . . _
This invention pertains to an improved process for coal
hydrogenation to produce hydrocarbon liquids and gases and
p~rtains particularly to a coal liquefaction and catalytic
hydrogerlation process which utilizes a petroleum-derived aro-
matic oil for slurrying the coal and increasing the yield of
naphtha and other light hydrocarbon liquid product
fractions.
Descri~tion of Prior Art
Numerous methods have been proposed in the prior art for
eec,ting the h~ydroconversion of coal into hydrocarbon liquid
and gas products. Present commercial conversion methods con-
~erltionall.y comprise subjecting a coal-oil sl'urry to
cataL~tic hydrogenation at elevated temperatures and pressure
c~orl~itions to produce a coal-derived synthetic oil and
distillate products and gas. Typically, these rnethods
utilize an ebullated bed catalytic reaction technique whereln
a strea~ of the coal-oil slurry is admixed with gaseous
hydrogen and passed upwardly through an ~bullated hed reactor
containing a bed of particulate hydrogenation catalyst,
thereby providlng for liquefaction and hydrogenation of the
coal. ~xamples of such prior art caal conversion processes
are those described in U. S. Patent Nos~ 3,519~555 to Keith
et al, 3,540~995 to Wolk' et al, 3 791,957 to Wolk, 3,607,719
~@~
3~i ```
to Johnson et al, 3,594,305 to ~ir~, 3,586,621 to Pitch,ord,
et al 3,755,13~ to Schuman, and 4,054,504 to Chervenak et
al.
Such techniaues, while aenerally effec-ti~e in convertino
coal into desired liquid products, have characteristically
been limited to conversion of the coal, while the oil pro-
viding the slurrying liquid needed for preparing and handling
the coal feed to -the pressurized reactor has remained
substantially unconverted throughout the hydroyenation
process. While the desirahility of effecting simultaneous
conversion of both coal and heavy crude or residuum oll feed
components in these ebullated bed procedures has been
recognized, for example, to increase the conversion effi-
ciencylof -the hydrogenation process nd to avoid reprccessing
the sLurrying oil stream through the reactor and equipment
trai.n, effective simultaneous conversion of the coal and spe-
cial oiL feedstock components has been generally considered
impracti.cal. Such consideratiGn was due in part to the dlf-
-erent reaction condltions believed necessary for the effec-
~ive converslon of the separate components, and also due to
the expectecl reLative incompatibility of the product Li~uids,
particularLy those comprising fu]l range distillates ~,oiling
up to about 1000F. Also, in coal liquefaction processes, it
has been thought necessary to achieve solvent oil balance,
i.e., to produce at least sufficient solvent oil -to slurry
the coal feed to the reactor and thus enhance its
liquefaction and hydrogenation reaction to produce desirable
hydrocarbon liquid products.
~ owever, it has now been unexpectedly found -that certain
petroleum-derived oils, such as clarified aromatic decant oil
recovered from catalytic cracking of petroleum crude, can be
~19 5;~i3 5i
advar.tac20usly used as a solvent or slurryina oil for the
par.iculate coal feed in a coal hydroaenation process The
une~ected bene.its of this process seauence is that a low
cost ~etroleum derivative which is difficult to utilize, can
be suc^ess'ullv used in the".~-Coal'~rccess to slurry t'ne coal
feed anc also to enhance the production of naphtha an~ liaht
distillate fractions by selective hydroconversion of the coal
and the decant oil feed.
SUMMARY OF INVENTION
_ _ _ _ _ _
This invention provides a coal catalytic hydrogenation
process for pr~ducing desirable hydrocarbon liquid and gas
products, in whlch a ~etroleum-derived liquid fraction is
advantageously used for at ~east part of the slurrying oil
for the particulate coal feed to the catalytic reaction zone.
More specifically~ the invention comprises a process ~or the
simultaneous catalytic hydrogenation of coal and a petroleum-
derived oil component of a fluid coal-oil feed blen~, wherein
both the coal and petroleum-derived oil components of the
feedstream are converted to hydrocarbon liquid ~roducts and
gases, and provides an increased Fercentage yield of the
O
desira~le C4- 650F naphtha and disti.llate oil fractions
product. Xn the invention, a fluid feedstock blend
comprising particulate coal and a petroleum derived oil
having a normal boiling range of about 300-lOO~F~ such as
aromatic ~ecant oil obtained from a petroleum catalytic
cracking step is contacted with hydrogen preferably in an
ebullated bed of commer~ial hydrogenation catalyst particl`es,
in general accordance with.conventional ebullated bed reactor
' . .
* Trademark
~ ~ 9 ~;i 6 3 Si
operation, as descrihed in U.S. Patent Re. 25,770, Although
the petroleum-derived oil fract.ion used has less desirable
coal solv~nt characteristics compared to coal-derlved oils 7
it unexpectedly facilitates the coal hydrogenation reaction
and increases the percentage yield of the naphtha and light
distillate product fractions.
DESCRIPTION OF INVEMTION
In the invention, finely divided coal, which may suitably
, .
comprise bitu~lnous, sub-bituminous or ]ignite-type coal, is
admixed with sufficient petroleum-derived oil comprising at
least about 5~ up to 100~ by weight of oil normally boiling
in range of about 300-1000F to provide a fluid coal/oil
blend. Hydroconversion of the coal and oil components of
this blend is achieved by feeding the heated blend with
hydrogen upwardly through a reaction zone, wherein it is
contacted by an ebullated bed of commercial hydrogenation
catalyst particles. In general, -the catalyst used may be any
~a~alyst useful for the hydrogenation of coal, and may
comprise metal oxides selected from the group of cobalt,
molybdenum, nickel, iron, tin, and tungsten, deposited on a
base support com~rising alumina, magnesia, silica, or
combinations thereof. Such particles are in the form of
beads, extxudates or pellets, and have a particle size of
0.050-0.200 inch, a bulk density of 30-50 lb/ft3~ and total
pore volume when fresh of 0.50 ~0,90 cc/gm.
The reaction zone conditions are maintained- at a tem-
peràture within the range of about 750~to 900F, and pre-
erably about 780~ to 8~0F, and at a hydrogen paxtial
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pressure of about 1000 to 5000 psia, and prefera'Dly about
1~00 to.4000 psig. The percentage of unconverted coal and ash
solids in the reaction zone can be controlled within a
desired ranye of 10 - 25 ~ ~ either by operating in a once-
t~rough mode with sufficient slurryino oil, or by recycling
to the reaction zone a portion of separator hottoms liquid
from which solids have been partially removed.
The coal feed rate or space velocity for the coal/oil
bLend contacting the catalyst particles ls maintained within
the range of about 5 - 60 pounds coal/hr/ft3 reaction zone,
a~nd preferably at L0 - 40 lb/hr/ft3. While some conversion
of both the coal and oil components may occur at space
velocities of the coal/oil blend above this specified range,
it has been found that in order to achieve the unexpected
improvement in the oil and coal conversion rates obtainable
by the process of this .invention, space velocities below
about ~0, and preferably within the range of about 10 to
about 40 pounds of coal per hour per cubic foot of reactor
voLume should be maintained. The reactor effluent materia.L
is wi.thdrawn overhead and passed to subsequent separation and
~ractlonation processing steps as desired.
In general, the proportions of petroleum-derived
sl.urrying oil to coal-derived oil used in the feedstock blend
are determined by product objectives and petroleurn-derived
slurrying oil availability. Broadly, at least sufficient
total slurrying oil is admixed with the particulate coal to
provide a sufficiently fluid blend to permit pumplng the
blend through the preheater and reaction system and to
provide acequate f].uidization of the catalyst bed.
Typically, oil to coal weight ratios of from about 1.0 to 4
pounds of oil per pound- of coal are employed; preferably,
: : 5.
E 3~;
from about 1.3 to about 3 pounds of oiL per pound-of coal
are used to maximize 'nydroconversion efficiency for both the
coal and oil components.
The petroleum-derived oil useful in this invention is
preferably an aromatic distillate bottoms oil recovered. from
a fluidized catalytic cracking. unit (FCC) of a petroleum
refinery, and which after catalyst particles have been
removed is also calLed clarified decant oil. Such oils
usually have a broad normal hoiling range of 300-1000F and
gravity of 3-6 API. Analysis of a typical suitable
clarified decant oil is provided in Table 1 below.
Such use of clari~ied decant slurrying oi1 produces an
increased percentage of naphtha and light distillate product
ractions. Thus, rather than operating the coal hydrogena-
tion process to produce sufficient coal-derived solvent or
slurryiny oil to obtain solvent balance for slurrying the
coal, we have urlexpectedly fo~nd that such clarified flecant
olL from a petrole~m refining operation can be advan-
tageously used as a slurrying oll stream for the coal fee-l,
~nd the process operating conditions and catalyst replace-
ment r~te can be adjusted to maximize the desired production
o naphtha and light oil (180 - 650F boiling range~
products As a percentage of total slurrying oil needed,
usLng bFtween about 10% and 80~ petroleum-derived solvent
with the balance being coal-derived oil is desirable.
In an alternate and preferred embodiment of this inven-
tion, selected heavy coal-derived liqui~ fractions are.
. .
recycled for blending with the finely divided coal and the
petroleum-derived decant oil. In this embodiment suf~icient
. .coa.l-derived oil, preferably compr-isiny residuum-containing
~3.~5~35i
oil having nor~al boilina temperature range of 700 975'F, is
recycled to ~he coal blen~ing step to provide a total oil to
coal ratio in the feedstock blend of at least about 1.3
pcunds of oil per pound of coal, and preferably a ratio of
from aDout 1.5 to 3 pounds of total oil per pound of coal.
In practice, this embodiment of the nventicn can be employed
when, for example, adequate petroleum-derived decant oil is
available an~ it is desired to minimi~e the percenta~e of
light coal-derived oil fraction used for slurrying ~he coal
so as to increase the yielAs of lower-boiling hydrocarbon
liquid products. In this event, an increased petroleum-
derived oil fraction can be used, such as comprising20-80 W ~ of the total slurrying oil.. However, when
insufficient ligh~ pçtroleum~derived slurrylng oil is
available, a greater percentage of higher boilina coal-
derived oil is recycled ~or use in slurrying the coal feed,
to provide a welght ratio of slurrying oil to coal in the
feedstock blend of at least about 1.5, ~/hich represents a
total feed blend composition of about 40% coal and about 60%
o~l by weight. Also, if desired, some of the naphtha
rac~ion product can be returned to ~he catal~tic cracking
step to produce gasoline.
BRIFF DESCRIPTION OF THE DRAWIMGS
Figure 1 is a schematic ~iagram showing one embodiment o~
the process of this invention, illustrating the principal
steps of the process when using a petroleum-derived oil for
slurrying ~he coal feed.
Figure 2 shows an alternate embodiment of the process,
illustratina the principal sters of the process when
.
56~
slurrying the coal with a mixture of petroleum-derived decant
oil and recycled heavy coal-derived oil.
Fisure 3 is a araph showing the general relationship
between decant slurrying oil used and yields of naphtha and
light distillate fraction products.
DESCRIPTION OF PREFERRED EM~ODIMENTS
As shown in Figure 1, bituminous coal such as Illinois
No. 6, Kentucky No. 11, or Wyodak which has been ground to a
parti.cle size smaller than about 50 mesh (U.S. Sieve Series)
is provided at ].0 and passed to a slurry mixing tank 12. The
cloal is blended with a petroleum-derived oil 14 from refinery
62, usually comprising clarifled decant oil obtained from a
petroleum refinery fluidized catalytic cracking step and
having a normal boiling range of about 350-900F. Such
blending is in a weight ratio of oil to coal at least
sufficient to provide a pumpable slurry mixture, and usually
is in a weight ratio range of oil to coa]. hetween about 1.1
to abollt 4Ø
The coal-oil blend frorn s].urry rnixing tank 12 is
pressurized by a pump 16, which pumps the hlend thro~gh con-
duit 17 together w.ith hydrogen at ].8 and through heater 19 to
an ebullated hed reactor 20 containing a bed 20a of par-
ticuLate commercial hydrogenation catalyst. The coal-oil
blend and hydrogen pass through flow distributor 21 and
upwardly through the catalyst bed at sufficient velocity to
expand the bed. The catalyst 20a, which may suitably
comprise particles such as .060 diameter extrudates of nickel
molybdate or cobalt molybdate on alumina or similar suppor~
635
material is e~panded by at least about 20~ and not over
about 150% of its settled height by ~he upflowing fluids, and
is '~ept in constant random motion during reaction by the
u2ward velocity of the coal-oil blend and hydrogen gas.
The coal-oil blend is passed upwardly throuah the reactor
20 in contact with the catalyst at a space velocity of about
5 to 60 pounds of coal/hour/cubic foot, and preferably from
about 10 to 40 pounds of coal/hour/cubic foot of reactor
volume. Reaction conditions are preferably within the range
of 780-870F temperature and 1200-4000 hydrogen partial
pressura. Reactor li~uid is recycled through downcomer
conduit 22, recycle pump 22a and upward through distributor
21 to mainfain sufficient upward llquid veLocity to expand
the bed and maintain the catalyst in random motion in the
liquid to assure intimate contact and complete reaction.
Fresh catalyst is usually added to the reactor at connection
23 as needed and used catalyst removed at 24.
In the reactor 20, simultaneous hydrogenation and con-
version of the coal and slurrying oil occurs with consumption
~f ~ome hydroqen. Also, because the petroleurn-derived oil
contains aromatLc compounds and has significant solvent
propertles affecting the coal, the hydrogenation reactions
may be achieved at a somewhat lower reaction temperature than
would otherwise be necessary.
From the reactor 20 effluent stream 25 is passed to hot
phase separator 26. The resulting gas portion stream 27 is
passed to hydrogen purification step 30, from which recovered
hydrogen 31 is recycled to the reactor along with make-up
hydrogen at 3~a as needed.
.
Liquid stream 28 is withdrawn, pressure-reduced at 29 and
passed to liquid--solids se~aration system 32, which can
5~;~,5
- `_omprise hydroclone or a solvent preclpitation system.
Overflow stream 33 containina reduced concentration of solids
is passed to fractionation system 34, wherein the liquid is
fractionated into product streams comprising gas naphtha,
liaht and middle range distillatesj and heavy residuum
boilina range oils containina unconverted coal and ash.
Specifically, streams from the 'ractionator 34 are withdrawn
as product gas at 35, C4-400 naphtha fraction at 36,
distillate liquid at 37, and a heavy fuel oil at 38. A por-
tion of bot~oms stream 38 from fractionator 34 can be
recycled to the reactor 20 via conduits 39 to help control
the percen-tage of unconverted coal and'ash solids in the
reactor within, a de~ired ran~e, typic,ally about 10 ~o 25 W %.
From separation step 32 underflow stream 39 is passed to
vacuum distillation at 40. Vacuum overhead stream 41 is
combined with stream 38 and vacuum bottoms material at 41a
can be used for coking7 or as feed material for hydrogen
production.
With reference to Figure 2, al alternate process embodi-
,ment is shown which ~s slmilar to Figure 1 but utilizes bothpetro].eum-derived decant oil and a heavy coal-derived recycle
oi..l for slurrying the coal feed. Sirnilarly as described
above, coal 10 and decant oil 14a obtained from fluidized
catalytic cracker 64 are blended in the mixing zone 12
pressurized by pump 16, and passed to the reactor 20 along
with hydrogen provided at 18. Similarly as for the Figure 1
embodiment, the coal-oil blend undergoes nydrogenation
reactions while passing upwardly through the ehullated bed of
catalyst particles. ReIatively simultaneous conversion of
the coal, petroleum~derived decant slurry oil and heavy coal-
derived oil occurs with the consumption of some hydrogen to
: produce lower boiling hydrocarbon liquids and gas.
: . . ~ - . . . - . .
3~i
. From the reactor 20 effluent strea~ is removed via con-
duit 25 and passed to hot phase separator 26. Resulting gas
stream 47 is passed to hydrogen recovery system 30, from
which hydrogen s-tream 31 ls recycled to the reactor 20 along
with fresh make-up hydrogen at 31a as needed
From separator 26 the liquid portion is withdrawn as
stream 28 and passed to low pressure separator 42. The bot-
toms liquid stream 43 goes to a liquid-sollds sepa.ration
~tep 44,. whi.ch preferably co~pri.ses mul.~iple hydrcclone~. A
portion 45 of the overflow stream containing reduced solids
concentration is returned to coal slurrying zone 12, and the
remainder 47 is passed to fractionation system 54.
Underflow stream 48 from solids separation step 44 is passed
to vacuum distillation at 60, from which a bottoms material
stream is removed at 61.
From the low pressure separator 42, the overhead liquid
is condùcted via a.conduit 53 to fractionation system 54 or
~ractionation into gas stream 55, naphtha fraction strearn
S~, and light or heavy distillate oil products 57. Bottoms
màterial 58 is withdrawn from the fractionator 54 and can be
recycled to the slurry tank 12 via conduit 59 as required.
In this Figure 2 embodiment of the invention, a portion
56a of naphtha fraction 56 from the fractionator 54 is
passed -to re~inery catalytic cracking step 64 to increase
.. . . .
the production of gasoline at 66- Also, a selected portion
of the product distillate from -the fractionator 54 can be
recycled to the slurry mixing zone 12 via conduit 59, to
pro~ide a portion of-the slurrying liquid for the coal. The
selected recycled oil portion, which preferably cornprises
residuum-containing oil, is recycled as required to provide
~ , . . . . . .
i3S
a total oil to coal weight ratio within the slurrying tank
12 of about 1.0 to 4, and preferably about 1.3 to 3.
This invention will be furt'ner described by reference to
the followin~ examples, which should not be regarded as
restricting its scope.
EXAMPLE 1
CoaL hydrogenation operations ~ere conducted in a bench
. - - , ~ . . . .
scale unit using Illinois No~ 6 coal mixed with slurrying
oil containing various percentages of .clarified petroleum~
derived decant oil recovered from a petroleum catalytic
cracker unit. The slurrying oil/coal weight ratio used was
about 2.~. A typical analysis for the Illinois No 6 coal
feecl is provlded in Table 1, and Table 2 provides typical
properties of the clarified decant oil used.
TABLE 1
TYPICAL AMALYSIS OF ILLINOIS NO. 6 COAL
Moisture, ~7 ~ 1.60
Ultimate Ana]ysis, W ~ (Dry 3asis)
Carbon 67.25
Hydrogen 4.~1
Nitrogen 1.02
Sulfur 4.85
Ash 9 93
Oxygen (Difference) 12.14
,, , . . . :
TABLE 2
TYPICAL PROPERTIES OF CLARIFIED DECANT OIL
Ash <0.1%
Conradson Carbon 6.5~
Ramsbottom Carbon 5.33%
Viscosity, SSU @ 100F 1123
Viscosity, SSU @ 210F 59
Hydrogen type analy~is by high resolution ~MR
% aromatic H2 - 25
aliphatic H~ 75
Compound types by Mass Spectometer analysis
. . .. .aromatic, V ~ . ~7 8
saturates V % 2.2
Gravity, API 4.4 5.0 5 3 5.1
True Boiling Point, F ! !
I~P 410 332 364 407
10~ 608 556 571 589
30~ 688 672 685 692
50% 760 756 768 766
70% 830 832 ~50 843
90~ 932 941 969 955
Carbon, W ~ 89.398a . 9089.39 89.72
Hydrogen, W ~ 8.68~.37 8.50 8.36
Nitrogen, W ~ -- 0.32 0.37 0.33
Sulfur, W % 1.391.04 1.05 1.06
The oiL-coal slurry and hydrogen were preheated and fed
into the lower end of an ebull.ated bed cataly-tic reactor
about 0.8 inch inside diameter by 10 fee-t ~ong. '~e cata-
}yst us.ed was a commercial arade containing cobalt-
molybdenum on alumina material. The reaction conditions
maintained for a straight-through operation without use of
recycle oll to the reactor and the average resul~s achieved
are provided in Table 3 beLow.
13
. .. . . :
~ 3~;
TABLE 3
BE~CH SCALE H-COAL OPERATIONS
USI~G PETROLEUM DECANT GIL FOR SLUPRYING COAL
Run .~o. 1 2 3 a
Slurrying Oil Used, W %
Decant 25 12 8 2
Coal-Derived 75 88 92 98
Weight ~atio Slurrying Oil/Coal 2 2 2 2
Reactor Temperature, F 840850850 850
H2 Partial Pressure, psig 18401850 1842 1835
Coal Space Veloci-ty, lb/hr/ft3 31.231.2 31.2 31.2
Catalys~ Age,
, ilbs coal/lbs cataLyst........ 580. .700 .~890. 10Q0.
Product Yields, lb/100 lb coal
Cl-C3 hydrocarbon gas 8 2 8.99.5 12.9
C4-400F naphtha 28~1 25 822.~ 15.5
40q-650F light distillate 18.416.9 14.5 16.1
65d-975F fuel oil 10.9 10.08.6 12.3
975~F+ residuum 8.4 12.620.8 18.6
Unconverted coal 4.8 4.23.5 4.1
Ash 10.5 10.510.5 10.5
Vent Gases and Water10.7 10-110.4 10.0
H2 Const~ption 6.5 5.66.0 _ 5.8
'r~al~ 106.5 105.6 106.0 105.8
The yield results for light oil fractions are also shown
plotted in Figure 3 vs. weight percent decant oil in the
sLurrying oil, It is noted that resu~ts of these runs
showed a definite trend for increased yields of -the
~esirabLe C4-400F and C4-650F product fractiorls with
increasing percentage decant oil used in the slurrying oil.
. - . ,, ~ : . . 1'1 ,
35i
The percentage of C4-650F naphtha and distillate oil
fraction produced was increased by more than wou].d have been
e~pected due to the a~lded petroleum decant oil alone, thus
indicating that an unexpected synergistic effect occurred
due to the reactions of the aromati.c decant oil in the
catalytic reaction zone to hydroconvert more of the coal
residuum oil to naphtha and light distillate product
fractions.
I . . . . . ........ . . .......................... . ..
EXAMPLE 2
Addltional larger pilot plant scale coal hydrogenation
operations were conducted using Illinois No. 6 coal mixed
with a slurrying oil containing an increased percentage of
petroleum-derived clarified decant oil reco.vered from a
petroleum refinery catalytic cracker uni-t. The oil/coaL
slurry and hydrogen were preheated to about 650F and fed
into the lower end of an S foot inside diameter ebullated
hed catalytic reactor operated in a recycle operational
mode, i.e. with some recyclQ of heavy hydrocarbon liquid
fraction to the coal slurrying step. The catalyst us~d was
the same specification cobalt-molybdenum on alumina support
material used in Example 1.
Table 5 shows a comparison of the feedstock slurries and
reaction conditions used and resultant product yields
obtained in the-hydrogenation,and conversion of the ~lend of
Il.linois No. 6 coal and petroleum-derived decant oil reco
vered from a catalytic crac~er unit.
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A LE 5
H-COAL PROCESS OPERATIONS
USI~G PETROLE~M DEC~NT OIL FOR SL~RRYI G COAL
Coal-Derived
Coal-~erived Oil plus
_ Oil Decant Oil
Slurrying Oil Used, W %
Decant 0 44
Coal-Derived 100 56
Weight Ratio ~Slurrying Oil/Coal 1.65 1.65
Decant Oil to Total Feed, W ~ 0 27%
Reaction Temperature, F840 840
H2 Partial Pressure, psig1600 1600
Coal Space.Velocity, . .. ..
lb/hr/ft3 reactor 31.2 31.2
CataLyst Age, lbs coal/lb catalyst 1000 8~0-1000
Product Yields, lb/100 lb coall
Cl-C3 gas - l l 11.2 11.2
C4-400F naphtha 18.4 23.1
400-650F light distillate 13.5 15.3
650-975F heavy distillate 7.0 8.4
975F+ residuum oil 26.7 21.4
Unconverted coal 3.5 3.5
Ash 11.2 11.2
Vent Gases and Water8.5 5.. 9
Hydrogen Consumption5.3 5.1
TotaLs 105.3 105.1
Based on the results shown in Table S, it is seen that
und~r very similar reaction condit.ions significant].y mor.e oE
t~e desirable C4-400F naphtha and 400-650F light
distillate ractions were produced w~en petroleum-derived
decant oil was used for slurrying the coal than when coal~
derived slurrying oil was used alone. Furthermore, it is
noted that `all yields and. comb.inations of yields were
increased when using about 44 W % decant oil in the coal
slurrying oil as compared to using all coal-derived
slurrying oil- The yield resu~ts are shown plotted in
~, . . . ~ .
Figure 3, .and -confirm the- trend o lncreased yie]ds of
C4-~50F ~roduct oil fraction with increasing percentage of
decant oil used in the slurrying oil.
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.~lthough we have disclosed certain preferred embodiments
of our invention, it is recognized that various modifica-
tions can be made thereto, all within the spirit and scope
of the invention which is defined by the following claims.
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