Note: Descriptions are shown in the official language in which they were submitted.
PROCESS FOR SEPARATION OF SOLIDS FROM LIQUID HYDROCARBONS
This invention relates to the processing of liquid
hydrocarbons and, more particularly~ relates to the removal of
insoluble material from liquid hydrocarbons.
Liquid hydrocarbons can include, for example, products
derived from liquefaction of a mixture of coal derived li~uids
or non coal derived liquids plus coal, with or without a
catalyst; or products derived from hydroprocessing of a mixture
of coal or non coal derived liquids, with or without a
catalyst; or combinations thereof.
Although the following description of the process of
the invention will proceed with reference to the processing of
products of liquefaction of carbonaceous material, it will be
understood that this description is exemplary only of the
process of the invention applied to the separation of solids
from the above liquid hydrocarbonsO
Liquid hydrocarbons can be classified into the basic
components of oils, asphaltenes and pre asphaltenes. Insoluble
solids may comprise one or more of mineral matter, ash, spent
catalyst and unreacted or undissolved carbonaceous residue.
The oils are soluble in hexane, the asphaltenes are insoluble
in hexane and soluble in toluene and the pre-asphaltenes are
insoluble in toluene and soluble in tetrahydrofuran.
Reactor products from liquefaction of carbonaceous
material, which is well known in the art for conversion of
(3
2.
solid carbonaceol~s material such as anthracite, bituminous and
sub-bituminous coal, lignite and peat, and other carbonaceous
material to liquid products are usually in the form of a slurry
which contains oils, asphaltenes, pre-asphaltenes and insoluble
solids.
Removal of insoluble solids from the products of coal
liquefaction is desirable to permit optimum recovery and
processing of liquid hydrocarbons. The presence of insoluble
solids leads to difficulties in the subsequent downstream
refining and upgrading of liquid hydrocarbons. Separation of
insoluble solids from the coal extract liquids is difficult to
effect due to the wide particle size range of the discrete
insoluble solids, the relatively high viscosity of the liquid
phase even at high temperatures, the small differences between
the density of the liquid phase and the density of the solids,
and the inherent characteristics of the constituents of the
coal liquefaction products.
The separation of discrete mineral matter such as
insoluble solids from the coal extract liquids remains a
continuing problem. Filtration provides for a high liquid
yield by means of washing with a light oil and subsequent
recovery of the light oil by drying of the filter cake and
separation from the filtrate. A dried filter cake contains
typically by weight 5 to 10% liquid product. That is, the cake
consists of 90 to 95% solids and 5 to 10% of the desired liquid
product on a dried solids cake basis. Filtration, although it
provides a good liquid yield, still has as drawbacks: slow
filtration rates, cost of pre-coat materials, and handling of
the filter cake. Centrifuges do not achieve as sharp a
separation of the solids as by filtration. Also, mechanical
problems arise in the continuous removal of solids due to their
abrasive and adhesive properties. A centrifuged 'solids cake'
typically still contains 50 to 55% of liquid product on a total
cake weight basis. Hydroclones achieve an even less sharp
separation and are at best used for pre-thickening purposes in
combination with other unit operations. Solvent extraction and
leaching have been used for removal of only part of the
solids. Coarser and heavier particles need to be removed by
other means~ Magnetic separation processes can only also
remove part of the solids. The organic compounds of coal are
3.
diamagnetic while the ash, i.e. inorganic mineral matter
compounds, are paramagnetic which makes it possible to separate
these by ma~netic means. However, the unconverted coal cannot
be separated. Shou J.K.P. and Collins D.J. describe these
problems in: "A Review of Solid-Liquid Separation Technology
in Coal Liquefaction Processes", Proceedings of the 28th Can.
Chem. Eng. Conf., Publ. by Can. Soc. for Chem. ~ng., Ottawa,
Canada, 1978.
Distillation or evaporation is a possible means of
separation. Very sharp separation can be achieved but liquid
carry-over must be minimized. The bottoms of such units
typically comprise 55% liquid product and 45~ solids, resulting
in substantial liquid losses. Coking is another process which
provides a sharp separation. However, a considerable amount of
liquid product is lost due to gasification of the light oil
fraction and due to coking of the heavier liquid hydrocarbon
products.
Anti-solvent deashing is a process whereby the solids
are co-precipitated with some of the asphaltene and
pre-asphaltene portion of the liquid liquefaction product due
to the solution equilibrium imbalance brought about by the
addition of an anti-solvent. The precipitated solids phase
typically comprises 55 to 60% liquid product. E~amples of such
processes are described in U.S. Patents nos 3,790,467;
3,852,182; 3,856,675 and 4,180,456. U.S. Patent 3,790,467 is
typical in disclosing the use of an anti-solvent to precipitate
from solution "quasi-solid" materials to cause an increase in
size of smaller solids for enhanced separation using size as a
separation parameter. Valuable liquefaction product thus is
lost or tied up with the solids fraction.
Critical solvent processes affect separation by the
greatly enhanced dissolving power of the solvent in the range
of pressure and temperature near the critical values for the
solvent. ~wo processes that apply this property are described
in U.S. Pat. Nos. 3,607,716 and 3,607,717. By proper choice of
solvent, pressure and temperature, such a process can
effectively produce separate process streams enriched in
solids, asphaltenes~ pre-asphaltenes, and oils. After recovery
of the critical solvent by evaporation, the solids phase
typically still comprise 35 to 40~ of the liquid product.
4.
The asphaltenes and pre-asphaltenes are considered to
be non-distillable in that they "crack" into gaseous and liquid
hydrocarbons and coke upon heating, with a poor liquid
recovery. If the asphaltenes and pre-asphaltenes are separated
with the insoluble solids from the oil by distillation,
anti-solvent deashing or critical solvent deashing, subsequent
recovery of the asphaltenes and pre-asphaltenes as liquid
product becomes as best marginal. For low rank coals, these
processes provide a low liquid yield.
According to the process of the present invention,
mixtures of liquid hydrocarbons and insoluble solids are
contacted with a volatile solvent compatible with the oils,
asphaltenes and pre-asphaltenes for solubilizing said oils,
asphaltenes and pre-asphaltenes as opposed to the above prior
art processes in which the solvent functions as anti-solvent or
a critical solvent. The said liquid hydrocarbons and solids
are contacted with the volatile solvent in stages to form a
carrier solution. The carrier solution is displaced by the
volatile solvent, preferably by a countercurrent or
crosscurrent contacting mode, to produce a slurry of insoluble
solids with volatile solvent substantially free of the said
liquid hydrocarbons to permit a separation and removal of said
insoluble solids by gravity settling, preferably under
centrifugal forces, such that a minimum of interstitial liquid
containing a minor amount of the liquid hydrocarbons is
discharged with the insoluble solids. The interstitial liquid,
composed largely of the volatile solvent, is substantially
recovered from ~he solids by evaporation.
The liquid hydrocarbons, including substantially all
the asphaltenes and pre-asphaltenes, are thus effectively
separated from the solids and can be in turn separated from the
volatile solvent for conventional processing. High losses of
the asphaltenes and pre-asphaltenes inherent in known
processes, particularly for low rank coals such as lignite
coals, are avoided.
In its broad aspect, the process of the present
invention for separating insoluble solids from liquid
hydrocarbons containing oils, asphaltenes and pre-asphaltenes
comprises the steps of contacting the liquid hydrocarbons
with a volatile solvent compatible with the oils, asphaltenes
5.
and pre-asphaltenes to solubilize the said oils, asphaltenes
and pre-asphaltenes to form a carrier solution; separating
insoluble solids from the carrier solution by gravity
separation and displacing said carrier solution from the solids
by volatile solvent whereby said insoluble solids are
discharged with interstitial volatile solvent; recovering said
volatile solvent from the residual solids; and recovering oils,
asphaltenes and pre-asphaltenes substantially free of insoluble
solids.
Gravity separation is applied, preferably by
centrifugal forces which accelerate the rate of separation,
utilizing the density differences between the insoluble solids
and liquid phase. The volatile solvent is contacted with the
liquid hydrocarbons in an amount in the range of about 10 to
about 250% by weight of the liquid hydrocarbons preferably in
countercurrent or crosscurrent stages applying centrifugal
forces to each stage whereby the final insoluble solids residue
is compacted with a minimum of interstitial liquid, said final
interstitial liquid comprised largely of the volatile solvent
for ease of recovery.
Coal liquefaction products are particularly suited for
the application of the process of the invention with the use of
a coal extract volatile solvent, said volatile solvent normally
being recovered for recycle. The coal liquefaction products
are processed for the asphaltene, pre-asphaltene and oils
recovery and recycle of the volatile solvent.
The accompanying drawing is a simplified schematic
flow diagram o~ the process of the invention applied to the
processing of coal liquefaction products, it being understood
that the scope of the invention is not to be limited thereby.
Referring now to the drawing, reactor products from
coal liquefaction are mixed with a compatible volatile coal
extract solvent intro~uced by line 52 either in pre-mixer 10 or
directly in separator 14. Contact of the reactor products with
the solvent is accomplished, preferably in a series of
multiple-stage countercurrent or crosscurrent mixers with the
application of gravity separation such as by the use of
centrifuges at each stage, such that the solids residue in the
final mixing and separating stage is contacted with fresh
volatile solvent for discharge of compacted solids residue
therefrom con~aining inters~itially volatile solvent
essentially free of coal liquefaction products. The use of
pre-mixer 10 assists in the solubilizing of the asphaltenes and
pre-asphaltenes by the volatile solvent. The multiple~stage
contacting can be effected in a single device having multiple
internal stages.
The volatile coal extract solvent is recovered from
subsequent processing to be described and is compatible with
the oils, asphaltenes and preasphaltenes. The volatile solvent
is prepared from a coal derived oil fraction having at least
80~ by volume distillation temperature between about 205 and
535C for compatibility with the coal liquefaction products.
A typical volatile solvent, shown in Table 1, comprises by
volume about 98.3% distillation temperature between about
205 to 515C.
TABLE 1
COAL EXTRACT SOLVENT
Density (g/cm3) 0.98 at 217 C
Viscosity (cp) 23.50 at 20C
Elemental Analysis Wt. (%)
C 89.0
H 9.5
N 1.0
S 0.0
O 0.5
Atomic H/C Ratio 1.28
Distillation Characteristics
Temp. Range ( C) Vol. (%)
- 205 1.2
205 - 275 21.3
275 - 350 37 r 5
350 - 450 31.5
450 - 515 8.0
515+ (Residue) 0.5
(38
The volatile coal extract solvent is contacted and
mixed with the reactor products in an amount by weight in the
range of about 10 to about 250%, preferably about 20 to about
100%, of the coal liquefaction slurry product. The quantity
employed will vary according to the particular volatile solvent
used and the characteristics of the reactor products which are
determined by the coal starting material and the manner of
liquefaction. Separator 14 is maintained at a temperature in
the range of about 50 to 350C under a pressure within the
range of sub-atmospheric pressure to about 3.5 MPa.
Separation 14 is effected by gravity separation, in a
conventional gravity settling vessel or in a centrifuge with
the application of multiplied settling forces, for separation
primarily according to differences in densities between the
homogeneous carrier solution comprised of solvent and
liquefaction products and the insoluble solids. The carrier
solution is recovered as an overflow substantially free of
solids and the solids recovered as an underflow, the amount of
underflow preferably being kept to a minimum such as by the use
of centrifuyal forces to compact the solids and to minimize the
volume of interstitial carrier solution at each stage and to
minimize the amount of volatile solvent escaping with the
solids at the last stage~
The underflow containing solids with interstitial
carrier solution, mainly volatile solvent, is withdrawn through
line 16 and fed to recovery unit 18, which may constitute part
of separator 14 or consist of a separate vessel in which the
volatile solvent is evaporated at a temperature within the
solvent boiling range. The evaporated solvent and any
contained liquefaction product are fed by lines 22, 25 to
series condensers 24, 26 with condensed product recycled to
separator 40, to be described, by lines 28, 30, or discharged
by line 32 as product.
The solids, substantially free of solvent, are
withdrawn from unit 18 as dried, friable, non-sticking solids
which may be crushed and conveyed by line 20 to a gasifier or
burner. Separation of oil, asphaltenes and pre-asphaltenes in
separator 14 from the solids is substantially complete due to
the effective separation of the liquefaction products
solubilized in the carrier solution and displaced by the
c~
8.
volatile solvent, substantially eliminating loss of coal
liquefaction product with solids in line 20.
The overflow of carrier solution from separator 14 is
fed through line 36 to separator 40 and mixed with a coal
derived light oil which is incompatible with the asphaltene and
pre-asphaltene materials. The carrier solution and said light
oil, such as light naphtha, are processed in separator 40 at a
temperature in the range of about 50 to about 150C at a
pressure of from atmospheric pressure to about 3.5 MPa, the
light oil being introduced in an amount by weight in the range
of about 30~ to about 100% of the carrier solution. The
addition of the incompatible light oil precipitates a
substantial part of the asphaltenes and pre-asphaltenes in the
form of an immiscible liquid and/or solid phase having a
greater density than the density of the carrier solution from
which they are precipitated.
The immiscible phases can be separated from each other
by gravity settling, preferably under centrifugal forces, to
produce a non-viscous liquid overflow and a sticky semi-solid
underflow comprised mainly of asphaltenes and pre-asphaltenes.
The underflow is withdrawn by line 42 and is: returned to the
liquefaction reactor, not shown, for further conversion into
lighter oils; discharged for use as a solids product with a low
ash content; or upgraded such as by hydrocracking into
distillable oils.
The liquid overflow from separator 40 is fed by line
44 to recovery unit 46 for stripping and recovery of the light
oil fraction by flash evaporation and fractionation, or by
distillation, for recycle by line 54 to separator 40~ The
bottoms are withdrawn by line 48 and discharged as product
through line 50 or recycled by line 52 to separator 14 or
pre-mix vessel 10. The bottoms of vessel 46 may be passed
through a hydroprocessor 49 to convert remaining asphaltene and
pre-asphaltene fractions to distillates and to increase the
hydrogen concentration, i.e. to regenerate the volatile
solvent. Replacement of light oil taken Erom the system by
removal of the two product streams 42, 50 can be made up by
coal extract oil from coal liquefaction through line 38.
The overflow of carrier solution from separator 14 may
be directly fed to alternative processing unit 58 instead of to
separator 40. The ~nit depicted by numeral 58 may be a
9.
hydrocracker from which the liquids are subsequently separated
in a distillation column into products, recycle oil for the
slurrying of coal, and recycle volatile coal extract solvent
compatible with the asphaltenes and pre-asphaltenes; a
distillation column for separation of overflow by boiling
range; or ~ solvent deasphalting process such as a propane
deasphalting process or Duosol process in which the asphaltenes
and pre-asphaltenes are separated from the solvent.
The process of the invention was carried out for the
processing of reactor product resulting from the direct
liquefaction of lignite in separator 14 and recovery unit 18.
Separator 14 was a batch centrifuge op~rated at 1500 G's at
atmospheric pressure with carrier solution maintained at
150C. The reactor liquid product consisted of 86.49 mass
units of liquid hydrocarbons and 13.51 mass units of unreacted
coal and ash. Contacting was carried out in a three-stage
crosscurrent mode using a total of 205.34 mass units of
volatile coal extract solvent. The last underflow was fed to a
vacuum flask for evaporation of the volatile solvent from the
residual solids. Table 2 indicates the distribution of
components in the feed to the separator, combined separator
overflow and final underflow and recovery unit overflow and
bottoms. For a feed to the separator of 86.49 mass units of
reactor liquid product, 1.84 units of reactor liquid product
were lost with the insoluble solids in the recovery unit
bottoms, resulting in a recovery of 97.99~ of the reactor liquid
product.
TABLE 2
SEPARATOR ¦
¦ UNDERFLOW I RECOVERY ¦ RECOVERY
¦ E'EED TO I SEPARATOR ¦ (FEED TO I UNIT I UNIT
CONSTITUENT ¦ SEPARATOR ¦ OVERFLOW ¦ RECOVERY ¦(OVERFLOW)I BOTTOMS
UNIT)
OIL I 65.67 165.14 10.53 1 _ ¦0.53
ASPHALTENES I 14.85 114.41 10.44 1 _ 1 0.44
PRE-ASPHAL- ¦
TENES I5.97 15.10 10.87 1 _ 10.~7
86.49 1~-4.65 l l 11.84
INSOI.UBLE
SOLIDS I13.51 10.00 113.51 1 _ ¦13.51
VOLATILE
SOLVENT I 205.34 1180.07 ¦ 25.27 ¦ 25.27
