Note: Descriptions are shown in the official language in which they were submitted.
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1 FIELD OF THE INVENTION
2 This invention relates to the enhancement of the
3 quality and quantity of liquid products obtained from solid
4 coal. More particularly~ this invention relates to a lique-
faction process wherein all or any portion of the liquid
6 product from coal liquefaction is sub;ected to pyrolysis in
7 a pyrolysis reactor~ preferably a fluid coking zone, and
8 high boiling liquids obtained in the pyrolysis reactor are
9 recycled to the coal liquefaction zone for further treatment
and conversion to lower boiling liquids.
11 BACKGROUND CF THE INVENTION
12 The treatment of solid c~al to obtain liquids
13 therefrom has been extensively developed and a variety of
14 coal liquefaction processes have been reported~ These pro-
cesses include solvent refining9 direct hydrogenation of
16 coal~ catalytic or noncatalytic hydrogenation in the presence
7 of a hydrogen donor solvent and catalytic or noncatalytic
hydrogenation in the presence of a vehicle or nondonor mater~
19 ial. In coal liquefaction~ conversion of the coal is norm-
ally effected at elevated pressures and elevated tempera-
21 tures, e.g., above 150C., preferably above about 250C ,
22 while solvent extraction is normally effected at room temper-
23 ature or temperatures up to the boiling point of the solvent
24 employed~
Coal li~uefaction processes wherein a coking zone
26 is incorporated to treat the heavier or bottoms portion of
27 the liquids from the liquefaction reactor have been exten-
28 sively reportedO The bottoms stream is sent to the fluid
29 coking zone from which light gases9 liquids and coke are
recovered. In the coking zone~ heavy liquids~ e,g., 10004F.+
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are removed from a distillation tower located immediately above
the coking zone for further conversion. Since coke precursors
include high boiling condensed ring aromatic molecules, the coke
precursors will be recycled to the coking zone. It has now been
discovered, however, that by recycling these heavy materials to
the liquefaction zone where the materials are treated under hydro-
genation conditions, the yield and quality of the liquid products
of the process are enhanced considerably.
SUMMARY OF THE INVENTION
10The present invention provides a process for producing -
liquids from a coal feed which comprises liquefying the coal in
a liquefaction zone under liquefaction conditions including the
- presence of hydrogen or a hydrogen donating material recovering
a liquid bottoms product from the liquefaction zone which com-
prises unconverted coal and coal derived liquids, passing the
liquid bottoms product through a flash vessel to remove flashed
liquids and thereafter passing the remainder to a coking zone
and coking therein at least a portion of the bottoms product,
the improvement which comprises recovering a high boiling stream
boiling at 1000F+ and having a Conradson Carbon content of at
least 15 wt.% from the coking zone and recycling at least a
portion thereof to said liquefaction zone.
More specifically, the invention relates to a process for
producing liquid from a coal feed which comprises:
(a) liquefying the coal in a liquefaction zone under lique-
faction conditions including the presence of hydrogen or hydrogen
donating material;
.. . . .
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(b) recovering a liquid bottoms product from the liquefaction
zone which comprises unconverted coal and coal derived liquids,
passing the liquid bottoms product through a flash vessel to remove
flashed liquids and thereafter passing the remainder to a coking
zone and coking therein at least a portion of the bottoms producti
(c) recovering a high boiling stream boiling at a temperature
of 1000F. and having a Conradson Carbon content of at least
15 wt.% and a recycle solvent stream boiling in the range of about
400 F-700 F from the coking zone;
(d) hydrogenating and recycling at least a portion of the
f recycle solvent stream for use as hydrogen donating material; and
(e) recycling at least a portion of the high boiling stream
to the liquefaction zone.
Now, in accordance with this invention, an improved process
~ ,:
for producing liquids from solid coal is provided which, in
essence, comprises a coal liquefaction zone and a pyrolysis zone,
~, preferably a liquid coking zone, wherein there is effective in-
teraction between the zones to enhance the quality and quantity
of useful liquid products and reduce the eoke make from the eoking
zone. Thus, a high boiling, preferably 1000F+, stream is re-
covered from the eoking zone and at least a portion thereof is
reeyeled to the liquefaction zone where it is further treated
under liquefaction conditions. In contrast to previous methods,
where the high boiling stream from the coker was recycled to the
coking zone for further conversion, the high boiling stream is
now substantially upgraded in the liquefaction zone before re-
turning to the coker. In the liquefaction zone, the high boiling
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1~8544
stream is subjected to liquefacti.on conditions which i.nclude an
environment for promoting hydrogenation reactions. As a conse-
quence, this high boiling stream is converted either to upgraded
and lighter boiling fractions (which may be subsequently removed
as liquid product by dis-
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3544
1 tillation) or to fractions containing a higher hydrogen to
2 carbon ratio~ In either case~ however, coke production in
3 the coking zone is measurably decreased since the high boiling
4 liquids (containing substantial amounts of coke precur~ors
s such as condensed ring aromatic structures) have been broken
6 down into lower boiling components (and removed) or to more
7 hydrogenated forms that are less susceptible to coke formation
8 and more susceptible to cracking to valuable liquid products~
9 Liquid product quality and quan~ity are thereby enhanced.
In various embodiments of this invention, a solid
coal is suitably prepared as by grinding and drying, slurried
12 in a vehicle, p~eheated3 and subjected to liquefaction condi-
13 tions~ Liquefaction generally comprises elevated tempera-
14 tures and pressures and the pre~ence of hydrogen either in
the molecular form or available from a hydrogen source) such
16 as a hydrogen donor diluent or solvent~ Generally, hydrogen
17 donors are rendered more effective in coal liquefaction when
8 some molecular hydrogen is also present. The products of
19 the liquefaction zone, light gasesg liquids and unconverted
coal (including ash) are recovered. Generally, the gases
21 are separately recovered and one or more liquid streams are
22 also separately recovered~ Thus, an intermediate boiling
23 liquid product stream containing light liquids, e,gO, naphthag
24 diluent for recycle, and product liquid for ~rther upgrad-
ing (as by hydrotreating, e.gO9 hydrocracking~ hydrodesul-
26 furization, reforming~ etc.) may be separately recovered
27 as well as a bottoms stream containing unconverted or unre-
28 acted coal and heavy liquids, The split between the inter-
29 mediate liquid stream and the bottoms stream will be one
virtually of choice since the coking zone will not normally
3~35~4
1 affect materials boiling below about 8001850F. but suffi-
2 cient liquid will be necessary in order to pump the bottoms
3 stream to the coker (as a slurry).
4 In the pyrclysis zone, the overhead vapors are
usually partially condensed and light gases, light liquids
6 and gas oils are recoveredO Heavy liquids, depending upon
7 the desired cut point, are usually recycled to the pyrolysis
8 zone for further conversionO In some instances, the heavy
9 liquids which are withdrawn are cooled, condensed in a
0 scrubber and récycled as a quenching medium to condense the
11 overhead vapors from the cokerO The quench also serves to
12 scrub any solids that remain in the overhèad vapors. In-
13 stead of internally recycling the heavy liquids (with or
14 without scrubbed solids) to the pyroLysis zone7 these heavy
liquids or a portion thereof are recycled to the liquefac-
16 tion zone for further t~eatment under liquefaction condi-
7 tions.
18 Generally, the cut point of the recycle heavy
19 liquids will be a matter of choice and can be raised since
these heavy liquids have some limited market value as fur-
21 nace fuel~ for asphalt manufacture, or disposal as heavy
22 fuels, eOg.~ bunker fuels~ when fluxed with lighter compo-
23 nents. In general, th~se heavy liquids may have a boiling
24 point above about 800Fo~ for example9 above about 900F.
Normally9 however~ the heavy liquids will be 950F+ materials
26 and preferably 1000F+ materialsO A portion of the h`eavy
27 liquids may be used as a quench by a recycle pumparound sys-
28 tem and thereby contain unconverted solids. In either case,
29 i.e., with or without solids~ at least a portion and pre-
ferably at least a major portion, of these heavy liquids are
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recycled to the liquefaction zone.
Coal to the process may be any type of coal, such
as bituminous~ sub-bituminous~ lignite, brown coal, etc.,
and is generally ground to a finely divided state. Coal
particles will generally be in the range of 1/4" to 325
mesh, U.S. sieve series scale. The use of partlcles about
8 mesh or smaller is normally preferred. A typical inspec-
tion of a coal suitable for use in this invention is shown
in Table I of U SO Patent 3,6179513
GenerallyD any type of liquefaction process, iOe.,
where substantial chemical reactions occur, can be utilized.
Thus, solvent refined coalD as typified by the Pittsburgh
~I and Midway Coal Company process (PAMCO process) can be em-
ployed as well as c~talytic or noncatalytic processes em-
ploying hydrogen donor solvents or non-donor solventsD A
source of hydrogen is necessary and hydrogen can be supplied
either as molecular hydrogen or from a hydrogen donor sol-
vent, e~g~, tetralin and related compounds, or both. Lique-
faction is generally effected at elevated temperatures and
pressures, eOgO~ 600-1000Fo~ 500-5000 psig, and the reac-
tion proceeds for a period sufficient to liquefy (as mater-
ials that are soluble in methylethyl ketone) a substantial
portion of the coal~ for example9 at least about 25% on a
moisture and ash free basis (mOaOfO), preferably at least
about 50%O
A preferred coal liquefaction process is the hydro-
gen donor solvent processD preferably conducted in the pres-
ence of hydrGgen9 that iS9 about Ool to 4 wt. C/o hydrogen
based on m.aOfO coal charged to the llquefaction zoneO The
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hydrogen donor solvent generally comprises a wide boiling
fraction, eOg., 375F. to about 800F. The boiling range
is not critical except insofar as maintaining the hydrogen
donor molecules of the solvent in the liquid phase during
liquefactionO Preferably, the solvent contains at least
about 30 wt. %, more preferably at least about 50 wt. % of
compounds that are well known hydrogen donors under lique-
faction conditions. ThusD the solvent is composed of both
donor and non-donor compounds.
Preferred hydrogen donor compounds include indane,
C10-Cl2 tetralins9 C12C13 acenaphthenes, di-, tetra-, and
octa-hydroanthracene~ and tetrahydroacenaphthene as well as
other derivatives of partially saturated hydroaromatic com-
pounds~ A typical inspection of a suitable donor solvent
obtained from coal liquefaction is shown in Table II of U.S~
3,617,513
The hydrogen donor solvent is employed in a weight
ratio of l/l and 4/1 based on coal charged to the liquefac-
tion zone, preferably 1/1 ~o 2/1
Liquefaction conditions for the donor solvent pro-
cess may vary widely, e.g., 650 to 1000Fo~ 300 to 3000 psig,
preferably about 700F~ to 900F~ and 1200 to 2500 psig~
The products of the liquefaction zone, regardless of the
liquefaction process employed~ will comprise light hydrocar-
bon gases along with some H2S, C0 and C02 and a slurry liquid
containing the unconverted or unreacted coal. The slurry
liquid is normally processed by flashing (which serves to
lower the pressure on the stream and remove, by vaporization,
a portion of the liquids contained therein) and distillation
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l and, generally, three liquid streams are recovered. That i8,
2 a product stream boiling below about 700Fo is recovered
3 and used for upgrading by normal refinery processes. A
4 second stream boiling between about 700 and 1000F. can al-
so be recovered and a portion thereof can be hydrogenated
6 and recycled to the liquefaction zone as hydrogen donor sol-
7 vent. The 1000F+ material can be introduced directly to
8 the coking zone. One skilled in the art will readily see
9 that various processing schemes can be realized for the
liquid product from the liquefaction zone. These will de-
ll pend on product demand~ recycle solvent, economics, etc.
12 However, to produce a 1000F.+ stream, a vacuum distillation
l3 tower is required. The cut point on a vacuum distillation
14 tower will be a matter of choice depending upon having
lS ` enough liquid to pump the bottoms stream to the coking zone
16 and whether operations dictate the cracking of some of the
17 heavy liquids from the liquefaction zone. Thus, the feed
18 to the coking zone could easily be an 800Fo+ stream, prefer-
.
19 ably a 900F.+ stream, more preferably a 950F.+ stream or
higher, e.g., 1000Foto
21 The pyrolysis zone can be any type of thermal crack-
?2 ing zone such as a delayed coker but is preferably a fluid
23 coking zone~ Fluid cokers are relatively conventional pieces
24 of equipment and have been described in available literature~
The bottoms stream slurry is fed directly into the coking
26 zone wherein a bed of heated coke particles is maintained in
27 a fluidized state The vaporous and gaseous products are re-
28 moved overhead as a coker distillate and fractionally dis-
29 tilled.
Heat for the coking reaction is suppliçd by con-
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1 tinuously removing a portion of the coke from the coking
2 zone and burning a part thereof in a coke burner with air.
3 The remaining heated coke particles are returned to the cok-
4 ing zone at a temperature about 100F. higher than the oper-
ating temperatures of the coking zone~ Coking zone operating
6 conditions can vary from 900 to 1300F~ or higher with pres-
7 sures of 0 to 75 psigo A superficial gas velocity 0.5 to
4.0 feet/second maintains the coke bed in a fluidized condi-
9 tion. The particle size of the coke ranges from about 10 to
o 1000 microns with a fluidized bed density of about 15 to 60
11 pounds per cubic foot, and a space velocity of about 0.1 to
12 10 w/hr~/w. The coke burner operates at similar pressures
13 and gas velocities but at temperatures slightly higher than
4 the ~ioking zone so as to provide heat for the endothermic
S coking reaction.
16 Referring now to the drawing, particulate coal i5
17 introduced by way of line 100 into a mixer 102 wherein it
18 is combinet with a recycle donor solvent stream introduced
19 by way of line 104 to form a coal/solvent slurry with a
weight ratio of about 1~2 solvents per weight of coal. The
21 slurry i8 conducted by way of line 106 to liquefaction zone
22 108 at typical liquefaction conditions of 840F/ and 1500
23 psig. Hydrogen (about 2 wt. % based on m.a.f. coal) is in-
24 troduced via line 110. Within the liquefaction zone 108 hy-
drogen is transferred to the coal and pyrolysis zone bottoms
26 recycle from the donor solvent. Additional hydrogen may be
27 required since hydrogen will be transferred to the bottoms
28 recycle as well as the coal. Thus, about 2 wt. ~/O hydrogen
29 based on recycle liquid will suffice.
The liquid product, including unreacted coal, is
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removed as a slurry via line 111 and transported to fluid
2 coker 114. The flash vessel 112 is utilized to lower the
3 pressure between the liquefaction zone 108 and the fluid
4 coker 114. F lashed liquids are removed as product via line
113 and the remainder is passed to the coker via line 1179
6 F}ash vessel 112 may be an atmospheric distillation tower
7 and may also represent an atmospheric and vacuum distilla-
8 tion tower where lighter components are removed~ The cut
9 point of the material, as mentioned, is one of choice but
lo is preferably 900F.+, more preferably 950F.~ or higher,
11 eOg., 1000F.+.
12 The slurry feed in coker 114 is subjected to c~ack-
3 ing conditions at about 1050/1100F. The coke bed is main-
14 tained in a fluidized condition by steam introduced via line
116. A portion of the coke from coker 114 is withdrawn via
16 line 118 and is carried through line 120 by an entraLning
17 gas stream such as steam in line 122 and introduced into coke
18 burner 126. Air in line 128 maintains the bed of coke in a
19 fluidized state and is also used to combust a portion of
20 the coke in burner vessel 126. Flue gas is removed via line
21 130 while hot coke particles are removed via line 132 en-
22 trained in a gas stream such as steam in line 134 and intro-
23 duced into the coker 114 by way of line 136.
24 The vaporous products from coker 114 pass upwardly
25 through a cyclone separator 140 where alst all of the en-
26 trained coke is separated and returned through the cyclone
27 dipleg to the fluidized bed in the coking zone. The vapor- !
28 ous products are fractionated in a distillation column (suit-
29 ably mounted directly above the coker vessel) and a heavy
30 liquid preferably boiling at 1000F.+ is withdrawn as the
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vapor via line 141, cooled on external heat exchanger 144
2 (which may be a scrubber and acts as a quench) and a portion
3 of the cooled condensed heavy liquid is reçycled to the coker
4 fractionator above coker 114 to act as a quench for the over-
head vaporous products. Another portion of the condensed
6 heavy iiquid is recycled to the liquefaction zone 108
through line 146 for further treatment under hydrogenation
8 conditions as previously mentioned~ Alternatively, a portion
9 of the heavy liquids may be reintroduced into the coking zone
for further coking treatment via line 158.
ll The fractionation may also be used to produce a
12 700/1000F. gas oil stream in line 138, a naphtha stream
13 boiling up to about 400F. in line 148 and a gas stream in
14 line 150. A recycle solvent stream boiling in the range of
about 400/700F~ is removed via line 152 and at least a por-
16 tion thereof is recycled for use as hydrogen donor solvent
17 by way of line 154~ Product may be recovered in line 156
8 for further upgrading.
19 The recycle solvent is hyd~ogenated in hydrogena-
tion zone 160 with hydrogen from line 162 in the presence
21 of a suitable hydrogenation catalyst, e.g., cobalt molybdate
22 supported on an alumina support, and under hydrogenation
23 fonditions such as temperatures ranging from about 650F.
~. .P
24 to 850F~, e.g., 700F., pressures ranging from about 650
to 2000 psig, e.g~, 1350 psig, space velocity of about 1
26 to 6 wjhr/w and a hydrogen feed per barrel of feed of about
27 1000 to 10,000 scf/barrel, e.gO, 5000 scf/barrel, Hydrogen-
28 ated so~vent is removed via line 164 and may be passed
29 through a flash separation zone 166 for the removal of hydro-
gen and light ends via line 168. The li~uid i8 then trans-
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1 ported in line 169 to stripper 190 where naphtha is removed
2 via line 1919 Solvent leaves the stripper via Line 104 and
3 is recycled into mixer 102~
4 If desired~ gaseous products from the liquefaction
zone 108 can be removed by line 170 passed through a separa-
6 tor 172 and a gas stream removed by line 174~ Light hydro-
7 carbons from the gas stream may be removed in line 176 and
8 introduced into the fractionating tower located above the
9 fluid coker 114 for fractionation along with the products
of the cokerO
In another embodiment, not shown~ a portion of the
12 coke may be removed from the coker or coke burner and reacted
3 with steam for the production of hydrogen which can then be
14 used within the process in liquefaction zone 108 and sol-
vent hydrogenation zone 160~
16 In a further embodiment, also not shown, the heavy
coker liquids m2y be mixed with fresh coal feed rather tkan
8 being directly in~ected into the liquefaction zone. The
19 plastic mix could then be fed to the liquefaction zone or
the mixing zone and may be a desirable way to move fresh
21 coal continuously into a high pressure vessel, eOg., lique-
22 faction zone.
23 EXAMP~E
24 The bottoms (1000Fo+ material, designated CSKB-
2s 7501) from a microlube distillation of the liquids produçed
26 during the coking of liquefaction bottoms (produced by
27 liquefaction of Illinois coal in the presence of hydrogen
28 and tetralin -- a donor diluent solvent) were liquefied in
29 a tubing bomb, The liquefaction conditions of the tubing
bomb were:
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1 2 tetralin/solid feed
2 800F.
3 130 minutes residence time
4 1~6 wt. % hydrogen gas
lS00 psig final pressure
6 The resultant liquefaction product was a homogen~
7 eous solution with low viscosity. 0~14 wt. Vb hydrogen gas
8 was consumed~ The liquefaction yields were:
9 H20 2~61%
gas 2. 89%
11 Cx 0~83%
12 Cl -C3 2 ~ 06h
13 solid residue 41.51b
14 liquid 53 ~ 13Z
The solid residue was based on cyclohexane insol-
16 uble. To correlate the cyclohexane insoluble to 1000F.+
17 m~aterial, a blank cyclohexane solubility test of the solid
18 feed was carried out. The blank test showed 5.0 wt. b of
19 solid feed are cyclohexane soluble. Thus, the 1000F.+
2~ material was estimated to be 41~5 + S~0 = 46~5Z and the
21 liquid yield 53rl3 ~ 5~0 5 48~13Z~
22 Analysis of the product was carried out by three
23 different techniques:
24 Original 1000F. Mater- Liquid Make
ial in feed wt. % feed as w~./O wt.
26 analyzed feed 1000F
27cyclohexane was 8~2 53~1 48~
28GC distillation 13~4 48~0 40~0
29mass spectrometer
30analysis 2900 62~1 46t6
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1 A conservative estimate is that under the ab~ve-
2 mentioned liquefaction conditions, 40 wt. % of additional
3 liquid can be made from the microlu~e distillation bottoms
4 of fluid coking liquids. The converted liquids represent
about 3.0 wt. % of fresh feed coal.
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