Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Ihis invention eoncerns a process for the manufaeture of
valuable olefins and aromatics from coal-derived feeds~ocks,
Olefins are currently manufactured from petroleum naphtha,
liquid petroleum gas or light hydrocarbon gases such as ethane
or propane. In the case of light hydrocarbon gases, the yields of
ethylene etc. are high but the yields of aromaties are low.
A petroleum naphtha, ~Ihich is essentially paraffinic and eontains
C5 to C10 eompounds, gives yields of aromaties suffieiently high
to mak~e processes based on naphtha a major souree of aromatics.
The proeess~for~making olefins and aromaties from petroleum
naphtha involves thermal cracking or steam eraeking at te~peratures
in the range 830 to 1000C for short residenee times, of the order
of seeonds. The gaseous oleflns produced contain acet~lenes and
dienes whieh require to be seleetively hydrogenated over preeious
metal eatalysts. The liquid produets from the eraeker, known as~
pyrolysis gasoline eontain si2nifieant amounts of gum presursors
whieh require to be seIeetively hydrogenated before extracting the ~
aromatics or beore use às a motor fuel. ~ ~ `
There are eurrently ~orldwide shortages of petroleum ~aphtha
and light hydroearbons from whieh to manufacture olefins and
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aromatics, and prices have increased substantially. Alternative
sources of feedstocks are required to replace the depletsd petroleum
feedstoc~s. The aim of the present invention is to provide a
process ~hereby lower olefins can be made in yields similar to
those from petroleum naphthas and whereby aromatics can be made in
yields which surpass those yields obtained from paraffinic
hydrocarbons derived from petroleum.
The present in~ention provides a process for the manufacture
of olefins and aromatics from coal-derived materials, the process
comprising
a) hydrogenating over a hydrogenation catalyst a coal-derived
oil fraction boiling within the range 170 to 300 C which
fraction contains at least 9~jO polynuclear hydrocarbons
and comprises a major proportion of naphthenes and contains no
significant amount of mineral matter to yield a hydrogenated
oil which is substantially completely saturated,
b) optionally stripping the hydrogenated oil of light ends
boiling below 170C and
c) cracking the hydrogenated oil product of step a) or step
b) to yield a product Oontaining olefins and liquid
rnononuclear aromatics.
Ihe coal-derived oil fraction starting material is preferably
the product of hydrocradkinga coal-derived oil, although other
coal-deri~ed starting materials of equivalent pro-certies may be
used~ Preferably the coal-derived oil is obtained by extracting
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a coal using a liquid solvent or a gaseous solvent; such
extraction methods are known in the art. Undissolved coal and
mineral matter ~e then separated, suitably by filtration or
centrifugation, since the mineral matter content of coal poisons
hydrotreatment catalysts. The coal may be a bituminous or brown
coal or lignite. The coal-derived oil may, however, be from a
source other than direct coal extraction. It may be, for example9
an oil from the pyrolysis or hydropyrolysis ~f coal, or R fraction
thereof, or may be an oil product or by-product stream or fraction
from a coal conversion process.
The catalytic hydrocracking of coal-derived oils has been
proposed in the art. Suitable catalysts are those of the type
Co or Ni and Mo or W sulphides, or a combination thereof, on a
catalyst support which maX be ~ alumina, clay, active carbon, zinc
oxide, magnesium oxide, alumino-silioates, silica~ chromia etc.
A number of hydrocracking catalysts of this type are commercially
available. The conditions are preferably selected to yield an oil
boiling between 50 and 450C, with less than 15,~ by wei~ht boiling
above 450 C. It is necessary to fra~tionate the hydrocracked oil
to select a fraction suitable for further processing according to
the invention. ~he cut points must be withi~ the range 170 to
300C, and are suitably 180 to 300C or 180 to 250C.
In step a) the hydrogenation catalyst may be a metal sulphide
from Group VI 3 or Group VIII B of the Periodic Table, and may be
identical to or different from the hy~rocracking catalys~ mentioned
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above. Alterratively, the hydrogenation catalyst may be a
supported precious metal catalyst (e.g. Pt, Pd, Rh1 Ru) or a
supported precious metal sulphide catalyst. Hydrogenation
conditions are selected according to the catalyst used, but
would generally be within a temperature range of 350 to 450 C
and a hydrogen pressure range of 50 to 750 bar, preferably 180
to 2~0 bar. Hydrogen concentrations are suitably in the range
of 40 to 9~b~ preferably 35to 9~o~ this being dependent upon
the source of hydrogen. Liquid hourly space velocities are
suitably in the range 0.1 to 8.o h 1, preferably 0.4 to 1.0 h 1.
The hydrogenated oil product is preferably stripped of the
small quantity of lower boiling fractions-produoed during
hydrogenation~ by fractionating to remove material boiling below
170 C, preferably removing material boiling below 180 C. The
resultlng feedstock is then cracked, suitably in a conventional
steam or thermal cracker. The cracking temperature i9 suitably
800 to 1000C, and the vapour residence time is suitably 0~1 to
2 secsD The product contains C2 to C4 olefins which are
separated in known manner from the product liquid and separated
into ethylene, propylene, buter~e and butadiene streams. Each
stream is then purified of dienes and acetylenes by selective
hydrogenation in known manner. Aromatics are also separated
from the product liquid and purified in known manner, to yield
benzene, toluene and xylenes plus other mononuclear aromatics.
In addition to the provision of a new feedstock and process
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for the production of olefins and aromatics, the invention offers
the advantage that the concenkration of troublesome dienes and
acetylenes in the product streams of olefins can he lower than
those typical of olefin streams made from petroleum fractions. ;
W~ have found that the 170 to 300C cut of hydrocracked
coal oil consists almost exclusively of bi-nuclear ccmpounds such
as naphthalenes, tetralins and decalins and their alkyl-substituted
derivatives. If this oil is directly cracked, we found only low
yields of olefins and mononuclear aromatics and the main product
was unwanted naphthalene. We discovered that further hydrogenation
of the hydrocracked oil was essential to oonvert the naphthalenes
and tetralins to decalins, which crack to produce the desired pro-
ducts in greater yields.
The stripping of light ends before cracking not onl~ re-
moves mononuclear and lighter materials which giYe lcw yields of
olefins but also yields fractions boiling in the range 80 to 170C ~-
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or 80 to 180 & which are valuable for other uses such as xeformer
feedstock for e~omatics n~nufacture and gasoline.
The invention may be more fully appreciated by reference
to the accompanylng schematic flow diagram, illustrating a process
according to the invention and including the production of coal oil
by liquid extraction of coal using as solvent a recycle oil pro-
duced in the prccess. As the individual unit pro oesses present no
difficulty to the skilled man, these are not described in detail
but are in accordance with the foregoing description of the
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process of the invention.
Raw coal is fed to the process as stream A and admixed with
solvent oil in an approximately 1:3 ratio; the solvent oil being
stream G which is the ~ 300C fraction from distillatio.n colu~n
/separator 3. ~he oil-coal mixture is digested by heating in a
digester generally i~dicated by 1. C1 - C~ gases formed during
digestion are taken off as stream B, and residues containing ash
and undissolved coal are filtered off and removed as stream C.
The filtrate coal oil, stream D, is passed to a catalytic
hydrocracker 2, which is supplied with make-up hydrogen ~ in
addition to recycled hydrogen from a later step in the process.
The product from the hydrocracker, together with a + 300 C fraction
K is fed to.distillation column/separator 3. From separator 3,
C1 C5 gases are taken off as stream F, - 180C liquids, largely
containing mononucIear aromatics are removed as stream I, the
desired cracking feedstock which is the 180 - 300 C cut is taken
off as stream H, and the ~ 300 C fraction is recycled, as has
been stated, as stream G.
Stream H is passed into a catalytic hydrotreater ~essel 4
together with hydrogen ~E). The hydrogenated product passes to
a distillation column/separator 5 in which it is separated into
a light fraction (-180C) which is added to stream Il and a
180 - 300 C fraction J which is passed to a thermal cracker 6.
~he product ~rom the cracker is passed to another distillation
column/separator 7, from which are taken a number-of streams.
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Stream Q, containing methane and unused hydrogen, is recycled and
mixed with the fresh hydrogen feed to the hydrocracker, 2.
Streams L, M and N containing respectively ethylene, ~ropylene
and butenes are passed through selective hydrogenators 8, 9 and ~;
10 to hydrogenate acetylene and diene impurities.
Stream P, containing C6 - C9 aromatics ls also seleotively
hydrogenated in vessel 11 to remove non-aromatic unsaturations.
The bottoms product, boiling + 1~0 C,is removed as stream K and
recycled upstream of the hydrocracker 2 and mixed with the feed
to the first distillation column/separatort 30
me invention will now be described by way of the following
non-limiting example. - ~
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A coal extract oil was hydrocracked in a small scale hydro-
cracking unit and the crude product was fractionated to give
fraction boiling in the ranges 170 to 250C and 250 and 300co
Samples identified as A and C respectively were taken from these
fractions. Other samples of each fraction were hydrogenated over
a sulphided commercial cobalt molybdenum on alumina catalyst at
435C and a liquid hourly space velocity of 0~5 h 1. The
hydrogenated products were again fractionated to give fractions
boiling in the ranges 170 to 250C and 250 to 300c and samples
identified B a~d D respectively were taken from these fractionsO
The composition of the samples A to D are given in Table 1 below.
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TABLE 1
Composition of Coal Derived Oils
Example _ _ ~ ~
Boiling range (&) 170-250 170 250 250-300 250-300 ;
2nd hydrogenation No Yes No Yes
(%) (%) (%) (%) ,'
substituted decalins ) 28.5 95.5 23.7 90.7
mDno cyclo-olefins ) 0.1 2.3 O.2 2.4
alkyl benzenes )
substituted tetralins ) 47
cyclohexyl benzene ) .9 2.1 30.9 5.1
dihydronaphthalenes 7.7 O.1 11.7 1.8
naphthalenes 10.7 0.1 16.2 0.1
diphenyl/acenaphthene 3.3 0.1 8.4 0.1
As can be seen from the above table, samples A and C have
a high concentration of alkyl tetralins whereas B and D are mostly
aIkyl decalins.
The four sample oils were thermally cracked in a labora-
tory cracker under the conditions shown in Table 2 below, whic~
table also shows the crackiny patterns for the cracked oils. It
will be noted from Table 2, that there is an increased yield of
ethylene from the hydrogenated oils B and D.
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T ~ 2
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Example . A B C ¦. D SRN~
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Cracki~g temp. ~ C) o60 860 860 860 810
Residence time (sec) 0.4 0.4 0.4 0.4 o~3
C~4 6.412.0 5-5 10~8 12.8
C2H4 9.123.1 7.5 21.5 29.3
C2H6 1.0 1.5 oO8 1.7 3.4
C~H6 ) 15~4
C3H8 )3.58.o 2.8 10.7 0.5
C4H6 ) 5~7
C4H8 ~ C4H10 ) 5.4
C2~I2 . 0.10.4 0.1 o.3 _
Benzene . 3.517.12.5 13.5 5.2
Toluene 1.95-3 1.3 5.1 4.7
m + p-~ylene ) 2.1
)1-7 3-o 1.1 2.8
o-xylene ) .
ethylbenzene _ _ _ _ o.6
total BTX 7.125.44.9 21.4 13.7
naphthalenes 31.4 5-9 24.2 7.8 ~
0:h~ 11 5 ~ 19.6 5- _
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includes indene, diphenyl, acenaphthylene, fluorene,
phenanthrene/anthracene
+ SRN - straight run petroleum naphtha (IBP - 170 C)
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A further run was performed by passing feedstock through
the laboratory cracker at 40 ml/min, at a cracking temperature of
800C, and hydrogenated coal middle oil as specified in the present ;
invention was compared with a petroleum gas oil blend of the same
boiling range. Ethylene yields were 17.81% for the coal oll and
21.83% for the yas oil; total BTX, including ethyl benzene, yields
were 20.54% for the coal oil and 9~29% for the gas oil.
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