U.S. patent number 3,607,716 [Application Number 05/001,690] was granted by the patent office on 1971-09-21 for fractionation of coal liquefaction products in a mixture of heavy and light organic solvents.
This patent grant is currently assigned to Kerr-McGee Corporation. Invention is credited to Jack W. Roach.
United States Patent |
3,607,716 |
Roach |
September 21, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
FRACTIONATION OF COAL LIQUEFACTION PRODUCTS IN A MIXTURE OF HEAVY
AND LIGHT ORGANIC SOLVENTS
Abstract
Coal liquefaction products are separated into a plurality of
fractions of varying softening points and molecular complexity in a
solvent mixture containing a heavy organic coal liquefaction
solvent and a light organic fractionating solvent having a critical
temperature below 800.degree. F. under elevated temperature and
pressure conditions. In one variant, coal is liquefied with a heavy
organic coal liquefaction solvent, the light organic fractionating
solvent is added to the solution thus produced, and thereafter the
coal liquefaction products are separated into a plurality of
fractions at elevated temperature and pressure. Preferred heavy
organic solvents include anthracene oil, tetralin, catalytic
cracker recycle stocks, thermally cracked stocks and lubricating
oil aromatic extracts, and preferred light organic solvents include
pyridine, benzene and hexane. In a preferred variant, a mixture of
the light and heavy organic solvents is recovered directly from the
final fractionating stage, the solvent mixture is separated in a
solvent separating vessel directly into a heavy organic solvent
phase and a light organic solvent phase, and the two solvent phases
are passed in heat exchange relationship with incoming solvent-rich
streams to preceding fractionating stages to recover the heat
content and produce cooled liquid heavy and light organic solvent
streams for recycle. The invention further provides a method of
separating finely divided insoluble material from products of coal
liquefaction present in a solvent comprising a heavy organic coal
liquefaction solvent.
Inventors: |
Roach; Jack W. (Oklahoma City,
OK) |
Assignee: |
Kerr-McGee Corporation
(Oklahoma City, OK)
|
Family
ID: |
21697333 |
Appl.
No.: |
05/001,690 |
Filed: |
January 9, 1970 |
Current U.S.
Class: |
208/431; 208/430;
208/424 |
Current CPC
Class: |
C10G
1/04 (20130101); C10G 1/002 (20130101) |
Current International
Class: |
C10G
1/04 (20060101); C10G 1/00 (20060101); C10g
001/00 () |
Field of
Search: |
;208/8,10 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gantz; Delbert E.
Assistant Examiner: O'Keefe; Veronica
Claims
I CLAIM:
1. A method of fractionating products of coal liquefaction into a
plurality of fractions comprising
treating an organic solvent solution of products of coal
liquefaction in a treating zone at an elevated temperature and
pressure to separate a fluidlike first heavy fraction of coal
liquefaction products from a lighter first solvent-rich phase
containing dissolved coal liquefaction products,
the organic solvent consisting essentially of a mixture of at least
one heavy organic coal-liquefying solvent having a critical
temperature above about 800.degree. F. and at least one light
organic fractionating solvent having a critical temperature below
about 800.degree. F.,
the light organic fractionating solvent being selected from the
group consisting of aromatic hydrocarbons having a single benzene
nucleus and normal boiling points below about 310.degree. F.,
cycloparaffin hydrocarbons having normal boiling points below about
310.degree. F., open chain mono-olefin hydrocarbons having normal
boiling points below about 310.degree. F., open chain saturated
hydrocarbons having normal boiling points below about 310.degree.
F., mono-, di-, and tri-open chain amines, carbocyclic amines
having a monocyclic structure, heterocyclic amines, and phenol and
its homologs,
the organic solvent solution containing the heavy organic
coal-liquefying solvent in an amount to dissolve the coal
liquefaction products,
the organic solvent solution containing at least two parts by
weight of the light organic fractionating solvent for each part by
weight of the heavy organic coal-liquefying solvent and the
dissolved coal liquefaction products,
the organic solvent solution of coal liquefaction products being
treated at a temperature of at least 400.degree. F. and the
temperature being sufficiently elevated to form a liquid-to-liquid
bulk interface between the first heavy fraction and the first
solvent-rich phase,
the temperature and pressure being adjusted to provide a light
organic fractionating solvent density in the treating zone of less
than about 0.65 g./cc., the solvent density being sufficiently low
to separate the first heavy fraction from the first solvent-rich
phase and sufficiently high to retain the remaining coal
liquefaction products in solution in the first solvent-rich
phase,
the first heavy fraction having a viscosity under the temperature
and pressure conditions existing in the treating zone whereby it is
flowable from the treating zone, and
withdrawing the first heavy fraction from the treating zone.
2. The method of claim 1 wherein said light organic fractionating
solvent is selected from the group consisting of pyridine, benzene
and hexane.
3. The method of claim 1 wherein
said organic solvent solution contains initially finely divided
insoluble material derived from coal during liquefaction,
the temperature and pressure are adjusted to provide a light
organic fractionating solvent density in the treating zone of about
0.40-0.65 g./cc. when separating the first heavy fraction,
a body of slurry containing the insoluble material and the first
heavy fraction is separated in a lower portion of the treating
zone, the body of slurry contains the first heavy fraction in an
amount to flux the insoluble material present therein under the
temperature and pressure conditions existing in the treating zone,
and
the slurry is withdrawn from the treating zone.
4. The method of claim 1 wherein said heavy organic coal liquefying
solvent is selected from the group consisting anthracene oil,
tetralin, catalytic cracker recycle stocks, thermally cracked
stocks, and lubricating oil aromatic extracts.
5. The method of claim 1 wherein said heavy organic coal-liquefying
solvent is catalytic cracker slurry oil.
6. The method of claim 1 wherein said light organic fractionating
solvent is selected from the group consisting of pyridine, benzene
and hexane, and said heavy organic coal-liquefying solvent is
selected from the group consisting of anthracene oil, tetralin,
catalytic cracker recycle stocks, thermally cracked stocks and
lubricating oil aromatic extracts.
7. The method of claim 6 wherein said heavy organic coal-liquefying
solvent is catalytic cracker slurry oil.
8. The method of claim 1 wherein
the first solvent-rich phase is further treated in a treating zone
under elevated temperature and pressure conditions to separate at
least one additional fluidlike heavy fraction of coal liquefaction
products including a fluidlike final heavy fraction of residual
coal liquefaction products which is separated from a lighter
organic solvent phase containing mixed heavy organic coal
liquefying solvent and light organic fractionating solvent,
the temperature and pressure are adjusted to provide a light
organic fractionating solvent density in the treating zone during
separation of the final heavy fraction not greater than about 0.35
g./cc. and sufficiently low to separate the residual coal
liquefaction products from the organic solvent phase,
the final heavy fraction having a viscosity under the temperature
and pressure conditions existing in the treating zone during
separation thereof whereby it is flowable from the treating zone,
and
withdrawing the final heavy fraction of residual coal liquefaction
products from the treating zone.
9. The method of claim 8 wherein the pressure in the treating zone
during separation of the first heavy fraction and at least one
additional heavy fraction including the final heavy fraction is
approximately the same, and the temperature of the organic solvent
is adjusted to provide the desired light organic fractionating
solvent density for separation of at least one additional heavy
fraction including the final heavy fraction.
10. The method of claim 8 wherein
the temperature and pressure of said organic solvent phase are
adjusted in a treating zone to provide a light organic
fractionating solvent density not greater than about 0.10-0.20
g/cc. and sufficiently low to form a light organic fractionating
solvent phase and a heavy organic coal-liquefying solvent
phase.
said heavy organic coal-liquefying solvent phase having a viscosity
whereby it is flowable from the treating zone, and
withdrawing said heavy organic coal-liquefying solvent phase from
the treating zone.
11. The method of claim 10 wherein
said light organic fractionating solvent phase is withdrawn from
the treating zone, and
at least one of said withdrawn solvent phases is passed in heat
exchange relationship with a coolant comprising at least one
relatively cool solvent-rich phase whereby heat is recovered.
12. The method of claim 8 wherein
at least one fluidlike intermediate heavy fraction of coal
liquefaction products is obtained by treating the first
solvent-rich phase in at least one treating zone under elevated
temperature and pressure conditions providing a light organic
fractionating solvent density therein which is less than that
existing in the treating zone when separating the first heavy
fraction and greater than 0.2 g./cc.,
at least one intermediate heavy fraction separate by this treatment
having a viscosity under the temperature and pressure conditions
existing in the treating zone whereby it is freely flowable
therefrom, and
withdrawing at least one intermediate heavy fraction from at least
one treating zone.
13. The method of claim 12 wherein
said organic solvent solution contains initially finely divided
insoluble material derived from coal during liquefaction,
the temperature and pressure are adjusted to provide a light
organic fractionating solvent density in the treating zone of about
0.40-0.65 g./cc. when separating the first heavy fraction,
a body of slurry containing the insoluble material and the first
heavy fraction is separated in a lower portion of the treating
zone, the body of slurry contains the first heavy fraction in an
amount to flux the insoluble material present therein under the
temperature and pressure conditions existing in the treating zone,
and
the slurry is withdrawn from the treating zone.
14. The method of claim 13 wherein the pressure in the treating
zone during separation of the first heavy fraction and at least one
additional heavy fraction including the final heavy fraction is
approximately the same, and the temperature of the organic solvent
is adjusted to provide the desired light organic fractionating
solvent density for separation of at least one additional heavy
fraction including the final heavy fraction.
15. The method of claim 14 wherein
the temperature and pressure of said organic solvent phase are
adjusted in a treating zone to provide a light organic
fractionating solvent density not greater than about 0.10-0.20
g./cc. and sufficiently low to form a light organic fractionating
solvent phase and a heavy organic coal-liquefying solvent
phase,
said heavy organic coal-liquefying solvent phase having a viscosity
whereby it is flowable from the treating zone, and
withdrawing said heavy organic coal-liquefying solvent phase from
the treating zone.
16. The method of claim 15 wherein
said light organic fractionating solvent phase is withdrawn from
the treating zone, and
at least one of said withdrawn solvent phases is passed in heat
exchange relationship with a coolant comprising at least one
relatively cool solvent-rich phase whereby heat is recovered.
17. A method of liquefying and fractionating coal comprising
intimately contacting each part by weight of coal in particulate
form with at least two parts by weight of a heavy organic solvent
consisting essentially of an organic coal liquefaction solvent
having a critical temperature above about 800.degree. F. to produce
a heavy organic solvent solution containing coal liquefaction
products and finely divided insoluble material,
the coal being contacted with the solvent in a liquefaction zone at
a temperature of about 550.degree.-1,000.degree. F. and under a
pressure providing a solvent density of at least 0.5 g./cc.
the temperature in the liquefaction zone being below the solvent
decomposition temperature and the solution thus produced containing
at least two parts by weight of the heavy organic solvent for each
part by weight of the coal liquefaction products,
withdrawing the heavy organic solvent solution of coal liquefaction
products from the liquefaction zone,
admixing at least two parts by weight of light organic
fractionating solvent with each part by weight of the organic
solvent solution of coal liquefaction products to produce a mixed
organic solvent solution of coal liquefaction products,
the light organic fractionating solvent consisting essentially of
at least one substance having a critical temperature below about
800.degree. F. selected from the group consisting of aromatic
hydrocarbons having a single benzene nucleus and normal boiling
points below about 310.degree. F., cycloparaffin hydrocarbons
having normal boiling points below about 310.degree. F., open chain
mono-olefin hydrocarbons having normal boiling points below about
310.degree. F., open chain saturated hydrocarbons having normal
boiling points below about 310.degree. F., mono-, di-, and tri-open
chain amines, carbocyclic amines having a monocyclic structure,
heterocyclic amines, and phenol and its homologs,
treating said organic solvent solution of coal liquefaction
products at an elevated temperature and pressure in a first
treating zone to separate a fluidlike first heavy fraction
containing coal liquefaction products and said finely divided
insoluble material and a first solvent-rich phase containing
dissolved coal liquefaction products,
the organic solvent solution of coal liquefaction products being
treated in the first treating zone at a temperature of at least
400.degree. F. and the temperature being sufficiently elevated to
form a liquid-to-liquid bulk interface between the first heavy
fraction and the first solvent-rich phase,
the temperature and pressure being adjusted to provide a light
organic fractionating solvent density in the treating zone of less
than about 0.65 g./cc., the solvent density being sufficiently low
to separate the first heavy fraction from the first solvent-rich
phase and sufficiently high to retain the remaining coal
liquefaction products in solution in the first solvent-rich
phase,
the first heavy fraction having a viscosity under the temperature
and pressure conditions existing in the treating zone whereby it is
flowable from the treating zone, and
withdrawing the first heavy fraction from the treating zone.
18. The method of claim 17 wherein said light organic fractionating
solvent is selected from the group consisting of pyridine, benzene
and hexane.
19. The method of claim 17 wherein
said organic solvent solution contains initially finely divided
insoluble material derived from coal during liquefaction,
the temperature and pressure are adjusted to provide a light
organic fractionating solvent density in the treating zone of about
0.40-0.65 g./cc. when separating the first heavy fraction,
a body of slurry containing the insoluble material and the first
heavy fraction is separated in a lower portion of the treating
zone, the body of slurry contains the first heavy fraction in an
amount to flux the insoluble material present therein under the
temperature and pressure conditions existing in the treating zone,
and
the slurry is withdrawn from the treating zone.
20. The method of claim 17 wherein said heavy organic coal
liquefying solvent is selected from the group consisting of
anthracene oil, tetralin, catalytic cracker recycle stocks,
thermally cracked stocks, and lubricating oil aromatic
extracts.
21. The method of claim 17 wherein said heavy organic
coal-liquefying solvent is catalytic cracker slurry oil.
22. The method of claim 17 wherein said light organic fractionating
solvent is selected from the group consisting of pyridine, benzene
and hexane, and said heavy organic coal-liquefying solvent is
selected from the group consisting of anthracene oil, tetralin,
catalytic cracker recycle stocks, thermally cracked stocks and
lubricating oil aromatic extracts.
23. The method of claim 22 wherein said heavy organic
coal-liquefying solvent is catalytic cracker slurry oil.
24. The method of claim 17 wherein
said first solvent-rich phase is withdrawn from the first treating
zone and is introduced into at least one additional treating zone
including a final treating zone,
the first solvent-rich phase is further treated under elevated
temperature and pressure conditions to separate at least one
additional fluidlike heavy fraction of coal liquefaction products
including a fluidlike heavy fraction of residual coal liquefaction
products which is separated in the final treating zone from a
lighter organic solvent phase containing mixed heavy organic
coal-liquefying solvent and light organic fractionating
solvent,
the temperature and pressure are adjusted to provide a light
organic fractionating solvent density in the final treating zone
during separation of the final heavy fraction not greater than
about 0.35 g./cc. and sufficiently low to separate the residual
coal liquefaction products from the organic solvent phase.
the final heavy fraction has a viscosity under the temperature and
pressure conditions existing in the final treating zone during the
separation thereof whereby it is flowable from the treating zone,
and
the final heavy fraction of residual coal liquefaction products is
withdrawn from the final treating zone.
25. The method of claim 24 wherein the pressure in the treating
zone during separation of the first heavy fraction and at least one
additional heavy fraction including the final heavy fraction is
approximately the same, and the temperature of the organic solvent
is adjusted to provide the desired light organic fractionating
solvent density for separation of at least one additional heavy
fraction including the final heavy fraction.
26. The method of claim 24 wherein
the temperature and pressure of said organic solvent phase are
adjusted in a treating zone to provide a light organic
fractionating solvent density not greater than about 0.10-0.20
g./cc. and sufficiently low to form a light organic fractionating
solvent phase and a heavy organic coal-liquefying solvent
phase,
said heavy organic coal-liquefying solvent phase having a viscosity
whereby it is flowable from the treating zone, and
withdrawing said heavy organic coal-liquefying solvent phase from
the treating zone.
27. The method of claim 26 wherein
said light organic fractionating solvent phase is withdrawn from
the treating zone, and
at least one of said withdrawn solvent phases is passed in heat
exchange relationship with a coolant comprising at least one
relatively cool solvent-rich phase whereby heat is recovered.
28. The method of claim 24 wherein
at least one fluidlike intermediate heavy fraction of coal
liquefaction products is obtained by treating the first
solvent-rich phase in at least one treating zone under elevated
temperature and pressure conditions providing a light organic
fractionating solvent density therein which is less than that
existing in the first treating zone when separating the first heavy
fraction and greater than about 0.2 g./cc.,
at least one intermediate heavy fraction separated by this
treatment having a viscosity under the temperature and pressure
conditions existing in the treating zone whereby it is freely
flowable therefrom, and
withdrawing at least one intermediate heavy fraction from at least
one treating zone.
29. The method of claim 28 wherein the pressure in the treating
zone during separation of the first heavy fraction and at least one
additional heavy fraction including the final heavy fraction is
approximately the same, and the temperature of the organic solvent
is adjusted to provide the desired light organic fractionating
solvent density for separation of at least one additional heavy
fraction including the final heavy fraction.
30. The method of claim 29 wherein
the temperature and pressure of said organic solvent phase are
adjusted in a treating zone to provide a light organic
fractionating solvent density not greater than about 0.10-0.20
g./cc. and sufficiently low to form a light organic fractionating
solvent phase and a heavy organic coal-liquefying solvent
phase,
said heavy organic coal-liquefying solvent phase having a viscosity
whereby it is flowable from the treating zone, and
withdrawing said heavy organic coal-liquefying solvent phase from
the treating zone.
31. The method of claim 30 wherein
said light organic fractionating solvent phase is withdrawn from
the treating zone, and
at least one of said withdrawn solvent phases is passed in heat
exchange relationship with a coolant comprising at least one
relatively cool solvent-rich phase whereby heat is recovered.
Description
BACKGROUND OF THE INVENTION
This invention broadly relates to a method of separating coal
liquefaction products into a plurality of fractions in a solvent
mixture containing heavy and light organic solvents under elevated
temperature and pressure conditions. The invention further relates
to a novel process for liquefying coal with heavy organic solvents
and thereafter fractionating the resultant products with light
organic solvents, and a method of separating finely divided
insoluble material from a solution of coal liquefaction products in
a solvent comprising a heavy organic solvent.
The potentially soluble substances in fossilized carbonaceous
materials such as coal are composed largely of high molecular
weight three-dimensional cyclic structures which contain
predominantly six-membered rings. For example, coal contains
bitumen and humin, which have large, flat, aromatic lamellar
structures that differ in molecular weight, degree of aromaticity,
oxygen content, nitrogen content and cross-linking, volatile
matter, fusain, mineral matter, sulfur and moisture. The sulfur
content may be present as pyritic sulfur, inorganic sulfates,
and/or organic sulfur compounds.
The mineral matter remains behind as ash when the coal is burned
and fusain, which is a mineral charcoal, is consumed during burning
at high temperatures in the presence of sufficient oxygen for
complete combustion. The presence of sulfur in the coal in
substantial quantities results in contamination of the atmosphere
with oxides of sulfur upon combustion, and highly corrosive
sulfurous acid and/or sulfuric acid is produced therefrom upon
reaction with atmospheric moisture. As a result, air pollution
regulations in metropolitan areas often require that the sulfur
content of fuels be reduced so as to control atmospheric pollution.
The mineral content of the coal may be 10-15 per cent by weight or
higher in some instances, and this reduces the B.t.u. value of the
raw coal per unit weight and increases transportation costs. There
is an additional cost when the coal is burned as the ash residue
must be removed and disposed of in some manner.
The presence of mineral matter, fusain and sulfur in substantial
quantities also reduces the value of the coal for specialized uses.
For example, if these substances are removed prior to coking, the
deashed coal thus produced may be used for preparing high purity
anode coke which has a substantially higher value than the usual
impure coke produced from raw coal.
For the above and other reasons, it is desirable to reduce the
mineral matter, fusain and sulfur contents of coal. One process
presently used for removing these substances involves solvation or
liquefaction of desirable coal constituents such as bitumen and
humin in a heavy organic solvent to produce a solution of coal
liquefaction products containing suspended finely divided insoluble
material. Thereafter, the undesirable insoluble constituents such
as mineral matter, fusain and inorganic sulfur are separated from
the solution prior to recovery of the deashed coal liquefaction
products.
The methods available heretofore for separating finely divided
insoluble material from a solution of coal liquefaction products in
a heavy organic solvent have left much to be desired. For example,
gravity settling has a number of disadvantages due in part to the
low settling rates encountered under ambient conditions of
temperature and pressure, and especially in instances where the
solution is somewhat viscous in nature. Filtration methods also
have disadvantages as the solution is often viscous at room
temperature and must be heated to obtain sufficiently fast
filtration rates. Plugging of the filter pores with finely divided
insoluble constituents is an additional problem. In instances where
the viscosity of the solution is sufficiently low, centrifuging is
usually satisfactory insofar as the physical separation of the
solids from the solution is concerned. However, centrifuging
equipment is costly and it is difficult to remove the lighter
micron-sized particles. As a result of the above and other
deficiencies, there has not been an entirely satisfactory method
available heretofore for separating suspended finely divided
insoluble materials from a heavy organic solvent solution of coal
liquefaction products.
As a general rule, heavy organic solvents are much more efficient
coal liquefaction solvents than light organic solvents. The
solvation of coal in a heavy organic solvent produces a mixture of
coal liquefaction products which differ greatly with respect to
their chemical and physical properties. For example, the
liquefaction products may vary from low-boiling liquids to solids
which are soluble in the organic solvent and have softening points
of 300.degree.-400.degree. F. and higher. The low-boiling liquid
products may be recovered by distillation, but a method has not
been available heretofore for separating normally solid coal
liquefaction products into a plurality of fractions having desired
softening points or other physical and/or chemical characteristics.
A satisfactory fractionating method would be very useful as coal
liquefaction products with widely differing properties could be
produced for specific end uses.
The present invention provides an efficient method of separating
ash constituents from previously prepared coal liquefaction
products, and/or fractionating previously prepared deashed coal
liquefaction products into a plurality of fractions. Additionally,
it is also possible to liquefy coal employing heavy organic
solvents which are very efficient coal liquefaction solvents, and
to thereafter deash and/or fractionate the coal liquefaction
products with a light organic solvent which is much less efficient
as a coal-liquefying solvent. Heretofore it has been necessary to
recover the solvents used by flashing, condensation of the vapor,
and fractional distillation. This prior art method of solvent
recovery involves the use of expensive equipment with high
operating costs as the utility requirements are excessive. The
present invention overcomes this disadvantage by providing for the
direct recovery of each solvent, whereby each solvent may be heat
exchanged with incoming solvent rich streams to recover heat and
produce separate cooled streams of liquid light and heavy solvents
for recycle.
It is an object of the present invention to provide a novel method
of separating products of coal liquefaction into a plurality of
fractions in a solvent mixture containing a heavy organic coal
liquefaction solvent and a light organic fractionating solvent
under elevated temperature and pressure conditions.
It is a further object to provide a novel method of fractionating
coal liquefaction products in a mixture of light and heavy organic
solvents wherein a mixture of the light and heavy organic solvents
is obtained from the final fractionating stage, and the solvent
mixture is separated directly into light and heavy organic solvent
phases which are recovered and passed in heat exchange relationship
with incoming solvent-rich streams to recover the heat content
thereof prior to recycle.
It is a further object to provide a novel process for liquefying
coal with a heavy organic coal liquefaction solvent, and then
separating the coal liquefaction products in the solution thus
produced into a plurality of fractions employing selected light
organic fractionating solvents at elevated temperature and
pressure.
It is a further object to provide a novel method of separating
suspended finely divided insoluble material from coal liquefaction
products present in a solvent comprising a heavy coal liquefaction
solvent.
Still other objects and advantages of the invention will be
apparent to those skilled in the art upon reference to the
following detailed description and the examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B of the drawings illustrate one presently preferred
arrangement of apparatus for use in practicing the invention. FIG.
1B is a continuation of FIG. 1A.
DETAILED DESCRIPTION OF THE INVENTION INCLUDING PREFERRED VARIANTS
THEREOF
The process of the present invention provides a method whereby
liquefied coal dissolved in a mixture of heavy dissolving solvent
and light fractionating solvent is introduced into a
deashing-fractionating vessel under temperature and pressure
conditions such that the solvent density of the light fractionating
solvent is about 0.40-0.65 g./cc. and sufficiently low to cause the
rejection or separation of a small amount of the heavy liquefied
coal constituents. The lighter mixed solvent-rich liquefied coal
solution exiting from the deashing-fractionating vessel may then be
introduced into at least one vessel, in the last of which the
temperature and pressure of the solution are adjusted to give a
light solvent density of about 0.10-0.20 g./cc. to yield a fluid
bottom fraction comprising the heavy solvent and any residual
dissolved coal, as well as a light fractionating solvent phase
which may be withdrawn and recycled for heat recovery and reuse in
the method. In those instances where more than one vessel is
employed, the light solvent densities prevailing in such
intermediate vessels are decreased progressively from that existing
in the deashing-fractionating vessel to that existing in the final
vessel to thereby provide a succession of heavy coal fractions of
decreasing softening point and a succession of correspondingly
lighter mixed solvent rich phases. In one variant of the invention,
the deashing-fractionating vessel and all subsequent vessels may be
operated at a pressure which is at or below the critical pressure
of the light fractionating solvent provided that the pressure,
temperature and enthalpy are controlled whereby the light solvent
densities set forth herein are maintained.
Referring now to the drawings, a heavy organic coal liquefaction
solvent to be defined more fully hereinafter is passed from solvent
surge vessel 10 to mixer 11 via conduit 12 at a rate controlled by
valve 14. Makeup solvent is supplied to heavy solvent surge vessel
10 via conduit 15 upon opening valve 16. In the variant to be
presently described, which includes liquefying the coal in heavy
organic solvent and thereafter fractionating the liquefaction
products in the presence of selected light organic solvents, finely
divided raw coal in storage vessel 17 is introduced into mixer 11
via conduit 18 at a rate determined by meter 19. The relative feed
rates of heavy solvent and coal may be controlled so that the
weight ratio of solvent to coal in mixer 11 is between about 1:1
and 20:1, and preferably between about 2:1 and 5:1. The best
results are usually obtained when the weight ratio of solvent to
coal is approximately 3:1.
The coal and solvent in mixer 11 are agitated with agitator 20, and
the slurry thus prepared is withdrawn via conduit 21 and
transferred by pump 22 to gas fired heater 23 where the slurry
flowing in coil 24 is heated to an elevated temperature which
preferably closely approximates the desired initial temperature of
solvation or liquefaction. In the variant presently described,
valve 25 in conduit 26 is open and valve 27 in conduit 28 is
closed, and the heated slurry is passed to liquefier 29 via conduit
26. While it is not essential, it is usually preferred to carry out
the liquefaction in the presence of added gaseous hydrogen. When
gaseous hydrogen is added, it may be passed into the slurry flowing
in conduit 21 upon opening valve 30 in conduit 31.
The liquefier 29 preferably operates under a superatmospheric
pressure which is determined by the overpressure of gaseous
hydrogen when present, the vapor pressure of the solvent at the
operating temperature, and/or the hydraulic pressure applied by
pump 22. The liquefaction temperature is determined by the initial
temperature of the slurry flowing in conduit 26 and by the
temperature control fluid which is supplied to coil 32 via conduit
33 at a rate controlled by valve 34 and withdrawn via conduit 35.
The solvent is contacted with the coal under the temperature and
pressure conditions existing in the liquefier 29 for a sufficient
period of time to solubilize extractable carbonaceous constituents
therefrom and produce a solution of coal liquefaction products
which contains suspended finely divided fusain, mineral ash and
other insoluble constituents. The resultant solution usually
contains relatively large amounts of dissolved normally solid
liquefaction products of widely varying softening points, and in
many instances little or no low boiling normally liquid products.
The solution is preferably but not necessarily substantially
saturated with respect to the dissolved coal liquefaction products
under the temperature and pressure conditions existing in liquefier
29, i.e., at the solvent density in the liquefier 29.
The solution of coal liquefaction products containing insoluble
constituents and gases is withdrawn from liquefier 29 via conduit
36 and after passing through reducing valve 37, is introduced into
degassing vessel 44 where it is degassed and then introduced into
mixer 38 via conduit 58. The excess hydrogen and other gases are
withdrawn from vessel 44 via conduit 73 upon opening valve 74.
Light organic solvent is withdrawn from surge vessel 39 and
transferred by pump 40 via conduit 41 to mixer 38 where it is
admixed with the solution flowing in conduit 58 to form a solution
of coal liquefaction products in the resultant mixed light and
heavy organic solvents. Makeup solvent is supplied to vessel 39 via
conduit 42 upon opening valve 43. The light organic solvent is
supplied to mixer 38 in an amount to provide a weight ratio of
light organic solvent to the solution of coal liquefaction products
between about 2:1 and 20:1, and preferably between about 2:1 and
10:1. The best results are usually obtained when the weight ratio
of light solvent to the solution is between about 3:1 and 4:1. The
light solvent in vessel 39 is normally below the operating
temperature of liquefier 29 and has a temperature whereby the
solution flowing in conduit 58 is cooled to approximately the
operating temperature of vessel 45.
The pressure on the solution flowing in conduit 36 is reduced while
passing through reducing valve 37 to approximately the desired
pressure of operation of deashing fractionating vessel 45. The
temperature and pressure conditions selected for operation of
vessel 45 are such that the density of the light solvent is
sufficiently low to cause the rejection or precipitation of a small
amount of the heavy coal liquefaction products. While the mechanism
is not fully understood, it is believed that the coal liquefaction
products thus rejected tend to coat or encompass the particles of
insoluble material, and this causes the surfaces of the particles
to be tacky so that they are much easier to agglomerate. The amount
of coal liquefaction products rejected as a heavy phase from the
solution in vessel 45 should be sufficient to coat and, with the
attendant solvent, aid in fluxing the insoluble particles, and
usually is no more than about one-two times the weight of insoluble
material. However, substantially larger amounts may be rejected
such as three-five times the weight of insoluble material.
The solution of coal liquefaction products in the mixed light and
heavy organic solvents is withdrawn from mixer 38 via conduit 46
and introduced into vessel 45 through header 47. The header 47 is
positioned a substantial distance beneath the liquid-to-liquid bulk
interface 48 which is formed under the existing temperature and
pressure conditions between the body of relatively heavy fluidlike
slurry 49 in the bottom portion of vessel 45 and the lighter
clarified solution of coal liquefaction products 50. The header 47
is provided with a plurality of spaced outlets 51 and the solution
is injected into the slurry 49 therethrough. The slurry 49 contains
suspended mineral ash, fusain, and other insoluble material in
finely divided form fluxed with solvent and coal liquefaction
products, and has a viscosity whereby it may be readily withdrawn
via conduit 52 at a rate controlled by valve 53, or by the
operation of a pump which controls the volume withdrawn. The slurry
49 is withdrawn at a rate to maintain the interface 48
substantially above the outlets 51 on header 47. The vessel 45 may
be maintained at the desired operating temperature by passing a
heat exchange fluid to coil 54 via conduit 55 at a rate controlled
by valve 56 and withdrawing it via conduit 57.
The solution introduced into vessel 45 is at an elevated
temperature and has a low viscosity, and the particles of coated
insoluble material settle out rapidly. Unexpectedly, injecting the
solution into the relatively heavy slurry 49 and passing the
solution therethrough aids in coating the individual particles of
micron-sized solids and in the agglomeration thereof to produce
much heavier and faster settling particles. As a result, the
clarified solution 50 in the upper portion of vessel 45 is
substantially free of insoluble material and it does not require
filtering or centrifuging to remove the last traces of solids.
The clarified solution 50 containing coal liquefaction products
substantially free of insoluble material is withdrawn from the top
of vessel 45 at a rate to provide a sufficient residence time to
assure adequate settling of the insoluble material, such as 1-30
minutes and preferably 5-15 minutes. The clarified solution 50 is
passed through heat exchanger 60 in heat exchange relationship with
a relatively warm stream of light organic solvent recycled through
conduit 61 to storage vessel 39, and a relatively warm stream of
heavy organic coal liquefaction solvent recycled through conduit 62
to surge vessel 10. The solution 50 is withdrawn from heat
exchanger 60 at a substantially higher temperature and preferably
at a temperature closely approximating the desired operating
temperature for equilibrium vessel 63, and is then introduced into
vessel 63 via conduit 59. The light solvent density existing in
vessel 63 is substantially less than that existing in vessel 45 due
to the higher operating temperature and the slightly lower pressure
resulting from the drop in line and heat exchanger pressure. The
differential in the solvent density is sufficiently large to cause
a fluidlike fraction 64 of heavy coal liquefaction products to
separate from the solvent-rich lighter phase 65 of residual coal
liquefaction products. The vessel 63 is maintained at a uniform
operating temperature which is sufficiently elevated to permit a
liquid-to-liquid bulk interface 66 to form between the heavy
fraction of coal liquefaction products 64 and solvent-rich phase
65. The temperature is maintained at the desired level by means of
a heat exchange fluid fed to coil 67 via conduit 68 at a rate
controlled by valve 69 and withdrawn via conduit 70. The
temperature and pressure conditions existing within vessel 63 are
selected to provide a light solvent density whereby a desired
percentage of the heavier material dissolved in the solution 50 is
rejected in the form of a fluidlike heavy fraction 64. The heavy
fraction 64 contains sufficient solvent to lower the viscosity and
allow it to be withdrawn via conduit 71 upon opening valve 72
without plugging the same. The light and heavy solvent contents of
the withdrawn heavy fraction 64 may be recovered for recycling in
the process by flashing, condensation of the vapor to produce
liquid mixed solvent and fractionating into light and heavy solvent
streams. The residue remaining after flashing the solvent is a hard
friable deashed coal fraction having a softening point of about
400.degree. F. or higher.
The solvent-rich phase 65 containing residual liquefied coal
products is withdrawn from the top of vessel 63 via conduit 75 and
passed through heat exchanger 76 in heat exchange relationship with
the relatively warm light and heavy solvents flowing in conduits 61
and 62, respectively. The solvent-rich phase 65 is withdrawn from
heat exchanger 76 at a substantially higher temperature and
preferably at a temperature closely approximating the desired
operating temperature for fractionating vessel 77, and is
introduced into vessel 77 via conduit 75. The light solvent density
existing in vessel 77 is substantially less than that existing in
vessel 63 due to the higher operating temperature and the slightly
lower pressure level resulting from the drop in line and heat
exchanger pressure. The differential in light solvent density
between vessels 63 and 77 is sufficiently large to cause a
fluidlike fraction 78 of residual liquefied coal products to be
rejected from the solvent-rich phase 79. The vessel 77 is
maintained at a uniform operating temperature which is sufficiently
elevated to permit a liquid-to-liquid bulk interface 80 to form
between heavy fraction 78 and the solvent rich phase 79. The
temperature is maintained at the desired level by means of heat
exchange fluid fed to coil 81 via conduit 82 at a rate controlled
by valve 83 and withdrawn via conduit 84. The temperature and
pressure conditions existing within vessel 77 are selected so that
a desired percentage of residual liquefied coal products of
intermediate softening point are rejected from the incoming
solvent-rich phase 65. The heavy phase 78 contains some solvent and
has a sufficiently low viscosity to be withdrawable via conduit 85
upon opening valve 86 without plugging the same. The solvent
content may be recovered for recycle by flashing, condensing the
vapor, and fractionating the resultant mixed solvent to produce
liquid light solvent and liquid heavy solvent. The residue is a
normally solid deashed coal product having an intermediate
softening point such as about 100.degree.-400.degree. F. in most
instances.
The solvent rich phase 79 containing dissolved light liquefied coal
products is withdrawn from the top of vessel 77 via conduit 90 and
passed through heat exchanger 91 in heat exchange relationship with
the relatively warm light and heavy solvent streams being recycled
through conduits 61 and 62, respectively. The solvent rich phase 79
is withdrawn from heat exchanger 91 at a substantially higher
temperature, passed to gas-fired heater 93 where it is heated to a
temperature closely approximating the desired operating temperature
for fractionating vessel 92, and is then introduced into vessel 92
via conduit 90. The light solvent density existing in vessel 92 is
substantially less than that existing in vessel 77 due to the
higher operating temperature and the slightly lower pressure level
resulting from the drop in line, heat exchanger and heater
pressure. The light solvent density differential between vessels 77
and 92 is sufficient to cause a fluidlike fraction of the remaining
liquefied coal products 94 to be rejected from the incoming solvent
rich phase 79, and to form a lighter phase 95 which contains a
mixture of the light and heavy solvents. The operating temperature
is sufficiently elevated to permit a liquid-to-liquid bulk
interface 96 to form between the rejected fraction 94 and the
solvent phase 95. A uniform operating temperature is maintained by
means of a heat exchange fluid fed to coil 97 via conduit 98 at a
rate controlled by valve 99 and withdrawn via conduit 100. The
separated fraction 94 contains sufficient solvent to lower the
viscosity whereby it is withdrawable via conduit 101 upon opening
valve 102 without plugging the same. The solvent content of the
withdrawn fraction 94 may be recovered by flashing, condensing the
vapor to produce liquid mixed solvent, and fractionally distilling
the mixed solvent to produce liquid light organic solvent and
liquid heavy organic solvent for recycling. The residue is a
deashed coal fraction which is usually semisolid to liquid at room
temperature.
Upon closing valve 120 in conduit 119 and opening valve 114, the
mixed solvent phase 95 is withdrawn from the top of vessel 92 via
conduit 103, passed through heat exchanger 113 in heat exchange
relationship with relatively warm light and heavy solvent streams
flowing in conduits 61 and 62, respectively, passed to gas fired
heater 104 where it is heated to a temperature closely
approximating the desired operating temperature for
solvent-separating vessel 105, and then introduced into vessel 105
via conduit 103. The density of the light organic solvent in vessel
105 is substantially less than that existing in vessel 92 due to
the higher operating temperature and the slightly lower pressure
level resulting from the drop line, heat exchanger and heater
pressure. The light solvent density differential between vessels 92
and 105 is sufficient to cause a heavy organic solvent phase 106 to
separate from the light organic solvent phase 107. The vessel 105
is maintained at an operating temperature which is sufficiently
elevated to permit a liquid-to-liquid bulk interface 108 to form
between the heavy organic solvent phase 106 and the light organic
solvent phase 107. Such operating temperature is maintained in
vessel 105 by means of a heat exchange fluid fed to coil 109 via
conduit 110 at a rate controlled by valve 111 and withdrawn via
conduit 112.
The heavy organic solvent phase 106 is withdrawn from the bottom of
vessel 105 via conduit 122 and, after flashing through valve 121 to
a lower pressure, is introduced into flash chamber 123 where
substantially all of its contained light organic solvent is
vaporized and withdrawn via conduit 124 and normally open valve
125. The vapor flowing in conduit 124 is passed to light organic
solvent recovery, and the heavy organic solvent is withdrawn via
conduit 62 and passed successively through heat exchangers 113, 91,
76 and 60 in heat exchange relationship with the relatively cool
solvent-rich phases flowing in conduits 103, 90, 75 and 59,
respectively. The solvent rich phases are heated and the heavy
organic solvent is cooled to below its flash point and introduced
into surge vessel 10 awaiting recycle. This method of operation
allows cool liquid heavy organic solvent to be recovered directly
from the solution of liquefied coal products flowing in conduit
103. As a result, the cost of heavy organic solvent recovery for
recycle is much lower.
The hot light organic solvent phase 107 is withdrawn from the top
of vessel 105 via conduit 61 and passed successively through heat
exchangers 113, 91, 76 and 60 in heat exchange relationship with
the relatively cool solvent-rich phases flowing in conduits 103,
90, 75 and 59, respectively. The solvent-rich phases are heated and
the light organic solvent phase 107 is cooled. The solvent flowing
in conduit 61 downstream of heat exchanger 60 is further cooled in
heat exchanger 115 by means of a coolant supplied by conduit 116 at
a rate controlled by valve 117 and withdrawn via conduit 118. This
method of operation allows cool light organic solvent to be
recovered directly from the solution of liquefied coal products
flowing in conduit 103 without flashing and condensing solvent
vapor. As a result, the cost of recovery of the light organic
solvent for recycle is much lower.
In instances where the heavy organic solvent has a high solvent
capacity for the liquefied coal products, a mixed light and heavy
organic solvent may be employed for both liquefaction of the raw
coal and fractionation of the resultant liquefied coal products.
Examples of solvent mixtures for liquefaction and fractionation
include anthracene oil, tetralin, catalytic cracker recycle oil
and/or lubricating oil extracts as the heavy organic solvent in
admixture with a light organic solvent such as pyridine, benzene,
and hexane. The light and heavy organic solvents may be present in
the solvent mixture in the same ratios as exist in the mixture in
mixer 38. In instances where a small amount of light organic
solvent is contained in the heavy organic solvent used for
liquefaction, such mixture may be the heavy phase 106 in vessel
105, recycled through heat exchanger 113, 91, 76 and 60, but
without any pressure reduction through valve 121 for light solvent
flashing and removal.
In instances where a mixed light and heavy organic solvent is used
for liquefaction and fractionation, valve 114 in conduit 103 is
closed, and valve 120 in conduit 119 is opened, and the mixed
solvent phase 95 is withdrawn from vessel 92 via conduit 103,
passed via conduit 119 to conduit 62, and then passed successively
through heat exchangers 91, 76 and 60 in heat exchange relationship
with the relatively cool solvent-rich phases flowing in conduits
90, 75 and 59, respectively. The cooled mixed solvent is then
introduced into solvent surge vessel 10 for recycle in the process.
The recovery of liquid mixed solvent in this manner has all of the
advantages noted above in recovering the light and heavy organic
solvents as separate liquid streams for recycle. In instances where
the mixed solvent is used, then light solvent need not be
introduced into mixer 38 via conduit 41 unless required to achieve
the desired ratio of light to heavy solvents. In general, the
remaining steps in the liquefying and fractionating steps remain
the same as previously described with the exception of substituting
the mixed solvent for the solvent previously used.
Referring again to FIGS. 1A and 1B of the drawings, previously
prepared coal liquefaction products dissolved in a heavy organic
liquefying solvent are withdrawn from vessel 17, and passed into
mixer 38 via conduit 8 and heater 9 at a rate determined by pump 7.
In mixer 38, it is admixed with light organic fractionating solvent
in the manner and ratio previously described. The solution of coal
liquefaction products in the mixed solvent is withdrawn via conduit
46, passed to header 47, and introduced into equilibrium vessel 45
through outlets 51.
The vessel 45 may be operated as previously described to remove
insoluble constituents which are withdrawn as a fluidlike phase via
conduit 52. In instances where the coal liquefaction products have
been previously deashed, very little if any insoluble material is
removed but passing the solution through vessel 45 assures that a
small amount of insoluble material is not present in the heavy coal
fraction produced in vessel 63. The coal liquefaction products
contained in the clarified solution 50 withdrawn via conduit 59 are
fractionated in vessels 63, 77 and 92 to produce heavy,
intermediate and light fractions which are withdrawn via conduits
71, 85 and 101, respectively, in the manner previously discussed.
The heavy and light organic solvents are also recovered for recycle
as previously discussed.
The carbonaceous material fed to mixer 11 and liquefied in
liquefier 29 may be coal, which preferably is of a rank lower than
anthracite, such as subanthracite, bituminous, subbituminous, and
lignite or brown coal. Peat also may be used in some instances. The
particle size of the coal may vary over wide ranges and in general
the particles only need be sufficiently small to be slurried in the
solvent and pumped. For example, the coal may have an average
particle size of one-fourth inch in diameter or larger in some
instances, and as small as -200 mesh (Tyler screen) or smaller. The
most practical particle size is usually between -30 mesh and -100
mesh as less energy is required for grinding and yet the particles
are sufficiently small to achieve an optimum rate of liquefaction.
The particle size is not of great importance, provided extremely
large particles are not present as the solvent penetrates the coal
particles and the extractable constituents are liquefied
rapidly.
The heavy organic coal-liquefying solvent has a critical
temperature above 800.degree. F. and preferably above 850.degree.
F. and prior art coal-liquefying solvents falling within this
classification may be used. Examples of suitable liquefying
solvents include cyclic hydrocarbons having normal boiling points
of about 400.degree.-1,000.degree. F., and preferably polycyclic
hydrocarbons containing at least two condensed benzene rings.
Polycyclic hydrocarbons having an aromatic-naphthenic fused ring
structure wherein a benzenoid ring and a nonbenzenoid or a
naphthenic ring adjacent thereto are fused are especially useful.
Specific examples of solvents include fused ring aromatic
hydrocarbons containing two, three and four fused benzene rings
such as tetralin, decalin, diphenyl, methylnaphthalene,
dimethylnaphthalene, fluorene, anthracene, phenanthrene, pyrene and
chrysene. Commercially available mixtures including one or more of
the above mentioned compounds may be derived from petroleum
refining operations and from other sources, such as the destructive
distillation of coal, coal tar and oils. Examples of preferred
mixtures include anthracene oil, catalytic cracker recycle stocks
such as light recycle catalytic cracker oil, heavy recycle
catalytic cracker oil, and clarified catalytic cracker slurry oil,
thermally cracked petroleum stocks, and lubricating oil aromatic
extracts such as bright stock phenol extracts. The boiling range of
the mixtures may be, for example, about 500.degree.-1,000.degree.
F. and preferably about 700.degree.-900.degree. F. Refractory
highly aromatic streams wherein the aromatic constituents contain
two or more fused benzene rings per molecule and make up at least
50 percent by weight of the stream are preferred, and for better
results the aromatic constituents should be present in an amount of
at least 80-95 percent by weight. Clarified catalytic cracker
slurry oil is especially useful.
Light organic solvents having critical temperatures below
800.degree. F., and preferably below 750.degree. F., are employed
as fractionating solvents. Light organic fractionating solvents
comprise one or more substances selected from the following
groups:
1. Cyclic hydrocarbons:
a. Aromatic hydrocarbons having a single benzene nucleus and
preferably six to nine carbon atoms, such as benzene, toluene, o-,
m-, and p-xylene, ethyl benzene, n-propyl or isopropyl benzene, and
monocyclic aromatic hydrocarbons in general having normal boiling
points below about 310.degree. F., and
b. Cycloparaffin hydrocarbons which preferably contain four to nine
carbon atoms, such as cyclobutane, cyclopentane, cyclohexane,
cycloheptane, and nonaromatic monocyclic hydrocarbons in general
having normal boiling points below about 310.degree. F.
2. Open chain hydrocarbons:
a. Open chain mono-olefin hydrocarbons having normal boiling points
below about 310.degree. F. and preferably containing about four to
seven carbon atoms, such as butene, pentene, hexene, and heptene,
and
b. Open chain saturated hydrocarbons having normal boiling points
below about 310.degree. F. and preferably containing about five to
eight carbon atoms such as pentane, hexane, heptane, and
octane.
3. Amines, including the following:
a. Mono-, di-, and tri-open chain amines which preferably contain
about two to eight carbon atoms such as ethyl, propyl, butyl,
pentyl, hexyl, heptyl, and octyl amines;
b. Carbocyclic amines having a monocyclic structure and preferably
containing approximately six to nine carbon atoms, such as aniline
and its lower alkyl homologs wherein the alkyl groups contain about
one to three carbon atoms and up to three alkyl groups are present
on each monocarbocyclic structure; and
c. Heterocyclic amines preferably those amines containing about
five to nine carbon atoms such as pyridine and its lower alkyl
homologs wherein the alkyl groups contain approximately one to four
carbon atoms and up to three alkyl groups are present on each
heterocyclic structure.
4. Phenol and its lower alkyl homologs, and preferably phenols
having six to nine carbon atoms. The alkyl groups may contain, for
example, one to three carbon atoms and up to three alkyl groups may
be present on each phenolic nucleus.
Pyridine, benzene and hexane are usually the preferred
fractionating solvents. Other preferred fractionating solvents
include light aromatic extracts of reformate obtained by extracting
a catalytic reformate by a number of commercial processes including
the UDEX process and aromatic or phenolic cuts in general which
have critical temperatures below 800.degree. F., including those
derived from the destructive distillation of coal or coal tar and
light oils. Still other commercially available mixtures including
one or more of the foregoing classes of compounds may be employed,
and in many instances the mixture need not be purified prior to
use.
The presence of added elemental hydrogen during the coal
liquefaction step is not necessary, but it is usually beneficial.
When hydrogen is added, the feed to the liquefier 29 may include
0.1-2 percent and preferably about 0.25-1 percent by weight of
hydrogen based upon the weight of the coal. The excess hydrogen
which does not enter into the liquefaction reaction may be
recovered from the coal liquefaction products and recycled if
desired, and thus higher percentages than 2 percent by weight of
the coal may be used such as up to 5 percent by weight or more. The
hydrogen content of the vapor phase in contact with the liquid
solvent phase may be about 5-50 percent and preferably is about
10-35 percent by volume, but it may be higher or lower as desired
in a given instance. As a general rule, the higher the partial
pressure of hydrogen, the faster the liquefaction reaction, as more
hydrogen is available in the solvent for transfer to the active
sites produced on the decomposing or depolymerizing coal.
The temperature employed in operating liquefier 29 should be
sufficiently high to result in a fast solvation rate. The upper
limit is the temperature at which the carbonaceous material is
coked and/or the organic solvent is decomposed substantially during
the period of treatment. The temperature of liquefaction may be
550.degree.-1,000.degree. F. for the most liquefying solvents and
coals, and preferably is at least 650.degree. F. to 700.degree. F.
In most instances, the temperature should be about
650.degree.-900.degree. F., and about 700.degree.-850.degree. F.
for best results. The solvation temperature should not be
sufficiently high to result in substantial coking within the period
of treatment. The coking temperature varies from coal to coal, and
coals having a higher rank usually have a higher decomposition or
coking temperature. Oklahoma bituminous coal cokes at about
800.degree.-840.degree. F., and the more volatile Wyoming coals at
a lower temperature such as 700.degree.-800.degree. F. In instances
where a tubular reactor is employed and a slurry of coal is passed
through the tubes on a continuous basis, then somewhat higher
solvation temperatures are suitable due to the dynamic nature of
the system. Also, the flow rates through the tubes may be
sufficiently fast to reduce coking on the tube surfaces.
The liquefying solvent is contacted with the coal in liquefier 29
for a sufficient period of time to solubilize a substantial amount
of the extractable constituents, such as about 0.2-2 hours. For
economic reasons, the contact period should not be more than about
1 hour, and preferably no more than 0.25-0.5 hour. Usually more
than 50 percent by weight of the coal is liquefied, and often up to
80-90 percent.
The minimum weight ratio of light organic fractionating solvent to
the solution of coal liquefaction products is about 2:1 by weight,
and the upper limit is practical in nature and may be as high as
20:1 There is little improvement in the sharpness of fractionation
beyond weight ratios of 5:1 and 10:1, and the lowest weight ratio
necessary to give a desired degree of sharpness of fractionation is
preferred as the cost of handling the solvent increases with the
amount used. Usually a weight ratio between about 3:1 and 5:1 is
preferred.
The pressure in liquefier 29 may be between about 400 and 10,000
pounds per square inch absolute (p.s.i.a.), and preferably is about
500-3,000 p.s.i.a. for most heavy organic coal liquefaction
solvents. The pressure should be sufficient to provide a solvent
density of at least 0.5 g./cc. and preferably at least 0.6 g./cc.
at the existing temperature. There is no upper limit on the solvent
density during liquefaction as the highest that can be achieved
under practical operating conditions gives improved results due to
the increased solubility of the coal liquefaction products. The
liquefying solvents defined herein have a solvent density of about
0.5-0.9 g./cc., and preferably about 0.6-0.8 g./cc. under practical
temperature and pressure conditions for operating liquefier 29. If
the liquefying solvent density is too low, then it is necessary to
resort to pressure to increase the density. Usually pressurized
hydrogen is preferred as a pressurizing medium, but inert gases or
gaseous mixtures may be employed such as nitrogen, argon and
helium. Also, the pressure existing in liquefier 29 may be imposed
by suitable hydrostatic means such as a high pressure pump.
In instances where the solution flowing in conduit 46 contains low
boiling normally liquid liquefaction products, as well as insoluble
constituents and/or dissolved liquefaction products which are
semisolid to solid at room temperature, then the low-boiling
products may be removed by fractional distillation prior to removal
of the insoluble constituents and/or fractionating the semisolid to
solid coal liquefaction products. As a general rule, the average
molecular weight and complexity of the coal liquefaction products
increase with the boiling points of the normally liquid products
and with the softening points of the semisolid to solid products,
and products having a similar boiling point or softening point also
tend to have similar physical and/or chemical characteristics.
It is possible to separate one or more distillate fractions of
normally liquid products by a prior art fractionating step which is
not shown in the drawings in the interest of clarity, and
thereafter separate the heavy oils, semisolid, and solid products
into a plurality of fractions by the method of the invention. While
the fractions may differ markedly in chemical and/or physical
characteristics, the products within a fraction may have similar
chemical and/or physical characteristics and it is possible to
produce fractions which are suitable for specific end uses. For
example, low boiling normally liquid fractions may be used as
fuels, and liquid fractions of higher boiling point may be
catalytically or thermally cracked to produce low boiling
distillates suitable for use as fuels. The slurry 49 withdrawn from
vessel 45 contains a high concentration of sulfur, mineral ash and
other undesirable constituents, but it is possible to use the
residue remaining after flashing off the solvent as a fuel for
firing boilers and the like in areas where air pollution is not a
problem. The heavy fraction of coal liquefaction products 64
withdrawn from vessel 63, after flashing off the solvent, is useful
as a solid fuel in metropolitan areas where air pollution
regulations require the use of low sulfur fuels. The fraction 78 of
coal liquefaction products of intermediate softening point
withdrawn from vessel 77 has a low sulfur content and it is useful
as a solid fuel in metropolitan areas. Additionally, vessel 77 may
be operated in many instances at a sufficiently elevated
temperature and low solvent density to separate a fraction having a
softening point below 200.degree. F. and preferably below
150.degree. F. which may be hydrofined and/or hydrocatalytically
cracked to produce liquid fuels. The fraction 94 of light coal
liquefaction products withdrawn from vessel 92 is normally
semisolid to liquid upon flashing off the mixed solvent, and it
likewise may be fed to a conventional catalytic hydrofining unit
and/or catalytic or hydrocatalytic cracker to produce low boiling
distillate fractions useful as fuels.
It is possible to bypass up to two of the vessels 45, 63 and 77 in
instances where the desired end products will permit it. For
example, when the solution flowing in conduit 46 contains an
unobjectionable amount of insoluble constituents, vessel 45 may be
bypassed and the solution flowing in conduit 46 may be introduced
directly into vessel 63. If insoluble constituents are not
objectionable in the heavy fraction 64, then vessel 45 may be
operated under the conditions described for vessel 63 to thereby
cause the separation of heavy fraction 64 and slurry phase 49
simultaneously in vessel 45, vessel 63 may be bypassed, and the
solution flowing in conduit 59 may be introduced directly into
vessel 77. Similarly, the heavy fractions 64 and 78 may be rejected
along with slurry 49 by operating vessel 45 under conditions
described for vessel 77, and the solution flowing in conduit 59 may
be introduced directly into vessel 92. It is also possible to
bypass vessel 63 and introduce the solution flowing in conduit 59
directly into vessel 77, and thereby separate the insoluble
materials in slurry phase 49 in vessel 45 and reject heavy phases
64 and 78 in vessel 77. Still other modifications may be made in
the fractionating scheme illustrated in the drawings and described
herein.
The vessels 45, 63, 77 and 92 are operated at a sufficiently
elevated temperature to form a liquid-to-liquid bulk interface
between the separated fluidlike heavy fractions 49, 64, 78 and 94
and the lighter mixed solvent-rich fractions 50, 65, 79 and 95;
respectively. The minimum temperature sufficient to form the
liquid-to-liquid bulk interface will vary somewhat with the mixed
solvent and the chemical and physical nature of the separated heavy
fractions and the lighter mixed solvent-rich fractions. For
example, the minimum temperature is at least 400.degree. F. and
sufficiently high to form the necessary liquid-to-liquid bulk
interface, which may be as high as 500.degree.-650.degree. F. with
some mixed solvents when separating heavy fractions. At lower
fractionating temperatures, a fraction may be precipitated, but the
fraction has a viscosity whereby it is not fluidlike and freely
flowable from the treating zone. The fractions precipitated at
lower temperatures are semisolids or solids which tend to plug the
apparatus as they are withdrawn and thus continuous operation is
very difficult or impossible.
The maximum temperature for operating vessel 63 at practical
pressures to separate a fraction containing coal solubilization
products having a softening point above 400.degree. F. is
approximately the critical temperature of the light organic
fractionating solvent, the pressure being adjusted simultaneously
to provide a light solvent density of about 0.05 g./cc. less than
that prevailing in vessel 45. At temperatures above this level, the
density change in the fractionating solvent is very rapid and coal
liquefaction products having lower softening points than about
400.degree. F. separate along with the higher softening point
materials, and this lowers the softening point of fraction 64. By
operating vessel 63 near the minimum fractionating temperature, it
is possible to separate a heavy fraction having a softening point
in excess of about 400.degree. F.
The selection of a specific fractionating temperature between
400.degree. F. and about the critical temperature of the
fractionating solvent provides a convenient means of separating
varying yields of heavy fractions of coal liquefaction products
having high softening points and a high degree of molecular
complexity. Inasmuch as some of the heavy constituents often have
objectionable characteristics for certain end uses, the invention
provides a convenient means for removing the objectionable heavy
fraction prior to recovery of the remaining lighter fractions. It
is also possible to operate vessel 45 at a temperature closely
approximating the minimum level for forming a liquid-to-liquid bulk
interface, and reject a small amount of heavy tarry coal
liquefaction products along with the insoluble constituents to flux
the same. Thereafter, the temperature may be raised in one or more
stages to a level approaching the maximum for separating fractions
having softening points of 400.degree. F. or higher, and additional
fractions having softening points above 400.degree. F. may be
separated at successively lower solvent densities.
In instances, for example, where the heavy fraction 64 has a
softening point of 400.degree. F. or above, then vessel 77 may be
operated at a temperature higher than about the critical
temperature at a solvent density of about 0.05 g./cc. less than
that prevailing in vessel 63 to separate a fraction having a
softening point below about 400.degree. F. Surprisingly, the
critical temperature of the fractionating solvent is not the
maximum temperature at which a fraction of coal liquefaction
products may be recovered. Under the proper pressure conditions,
the upper temperature limit is the decomposition temperature of the
fractionating solvent and/or the solution of coal liquefaction
products. In instances where the temperature is significantly
higher than the critical temperature of the fractionating solvent,
then the fraction of liquefaction products usually has a lower
softening point, such as below 100.degree. F.
The vessel 92 is preferably operated above the critical temperature
of the light fractionating solvent to separate the remaining
dissolved coal liquefaction products as a heavy phase 94 from the
lighter phase 95 of mixed solvent. Vessel 92 may be operated at
essentially the same pressure as vessel 77, and the temperature may
be increased to a value such that the density of the light
fractionating solvent is about 0.2 g./cc. at the prevailing
pressure. Similarly, vessel 105 may be operated at about the same
pressure as vessel 92, and the temperature may be increased to a
value such that the density of the light fractionating solvent is
reduced to about 0.10-0.20 g./cc.
The following specific examples further illustrate the
invention.
EXAMPLE I
One hundred pounds per hour of Oklahoma Stigler seam coal having a
particle size of -65 mesh, a volatile matter content of 25.8 weight
percent, a fixed carbon content of 63.0 weight percent, and an ash
content of 12.1 weight percent is transferred from vessel 17 to
mixer 11 and admixed therein with 300 pounds per hour of anthracene
oil transferred from vessel 10. The mixture is slurried and
transferred by pump 22 to heater 23 via conduit 21, into which 4
pounds per hour of hydrogen is introduced immediately upstream of
heater 23. The heated slurry is withdrawn via conduit 26 and
introduced into liquefier 29. The residence time in liquefier 29 is
one hour, the temperature is 750.degree. F., and the pressure is
1,200 p.s.i.g. Under these conditions, the density of the
anthracene oil is 0.82 g./cc. and 85 weight percent of the coal is
dissolved.
The solution of liquefied coal products in anthracene oil
containing insoluble constituents is withdrawn from the bottom of
liquefier 29 via conduit 36 and passed through pressure reducing
valve 37 where the pressure is reduced to approximately 1,000
p.s.i.g. The mixture is introduced into degassing vessel 44, and
hydrogen, light hydrocarbons and other gaseous constituents are
separated therefrom and withdrawn via conduit 73. The degassed
solution is withdrawn from vessel 44 via conduit 58 and passed into
mixer 38 where it is admixed with a stream of pyridine flowing from
surge vessel 39 via conduit 41 at the rate of 1,500 pounds per
hour. The temperature of the pyridine stream is adjusted by means
of heat exchanger 115 to a value such that, upon admixture with the
deashed coal solution flowing in conduit 58, the resultant
temperature in mixer 38 is 560.degree. F. Under the prevailing
temperature and pressure conditions of 560.degree. F. and 1,000
p.s.i.g. respectively, the density of the pyridine is 0.62
g./cc.
The solution of coal liquefaction products in the mixed solvent is
withdrawn from mixer 38 via conduit 46 and introduced into
deashing-fractionating vessel 45 by means of header 47 and outlets
51 as illustrated in the drawing. Under the conditions prevailing
in vessel 45, a small amount of the coal liquefaction products
previously in solution are separated out, and a slurry phase 49 is
formed in the bottom of vessel 45. The heavy slurry phase 49 is
withdrawn as a fluid phase from vessel 45 at a rate of 50 pounds
per hour. It consists of 25 pounds per hour of pyridine and 25
pounds per hour of a mixture of the ash mineral content of the coal
and separated coal liquefaction products to flux the same.
The deashed solution of coal liquefaction products in the mixed
solvent phase 50 is withdrawn from vessel 45 via conduit 59, heated
to a temperature of 620.degree. F. by passing through heat
exchanger 60, and then introduced into vessel 63. At the existing
temperature and pressure of 620.degree. F. and 975 p.s.i.g.
respectively, the density of pyridine is 0.57 g./cc. Two fluid
phases form in vessel 63, the heavy phase 64 of which is withdrawn
via conduit 71 at a rate of 60 pounds per hour, of which 30 pounds
per hour is pyridine and the remainder is a heavy deashed coal
fraction which has a softening point in excess of 400.degree. F.
upon flashing off the pyridine solvent. The heavy deashed coal
fraction has a volatile matter content of 29.6 weight percent and a
fixed carbon content of 66.2 weight percent.
The lighter solvent-rich phase 65 remaining in vessel 63 is
withdrawn via conduit 75, heated to a temperature of 700.degree. F.
by passing through heat exchanger 76, and then introduced into
vessel 77. The density of the pyridine in vessel 77 is 0.23 g./cc.
A heavy phase 78 separates in vessel 77 and is withdrawn as a fluid
phase via conduit 85, at a rate of 40 pounds per hour, and
containing 20 pounds per hour of pyridine and approximately 20
pounds per hour of liquefied coal product. Upon flashing off the
pyridine solvent, this intermediate coal liquefaction product has a
softening point of 250.degree. F., a volatile matter content of
77.8 weight percent, and a fixed carbon content of 20.2 weight
percent.
The solution of coal liquefaction products 79 is withdrawn from the
top of fractionating vessel 77 via conduit 90, heated to a
temperature of 755.degree. F. by passing through heat exchanger 91
and heater 93, and the heated solution is introduced into vessel
92. The pyridine density is 0.17 g./cc. in vessel 92. The heavy
phase 94 settling in the bottom of vessel 92 is withdrawn therefrom
as a fluid phase via conduit 101 at the rate of 50 pounds per hour,
and it consists of equal parts by weight of pyridine and a light
coal liquefaction product fraction. Upon flashing off the pyridine,
the light coal liquefaction product remains liquid at room
temperature, and it has a volatile matter content of 83.9 weight
percent, an ash content of less than 0.1 weight percent, and a
fixed carbon content of 16.1 weight percent.
The light phase 95 in vessel 92 contains mixed anthracene oil and
light pyridine solvents. The light phase 95 is withdrawn via
conduit 103, further heated in heat exchanger 113 and heater 104 to
a temperature of 820.degree. F., and then introduced into solvent
separating vessel 105 in which the pyridine density is 0.14 g./cc.
The anthracene oil separates as a heavy phase 106, and it is
withdrawn as a fluid phase via conduit 122 at a rate of 300 pounds
per hour in admixture with an equal weight of pyridine and
introduced into flash chamber 123. Upon flashing off the pyridine
content, the anthracene oil has a volatile matter content of 99.3
weight percent, an ash content of less than 0.01 weight percent,
and a fixed carbon content of 0.53 weight percent. The light phase
107 withdrawn via conduit 61 consists essentially of pyridine, and
it is passed in succession through heat exchangers 113, 91, 76, 60
and 115, the first four being in heat exchange relationship with
the incoming streams to vessels 105, 92, 77, and 63, respectively,
and is then introduced into surge vessel 39 for recycle. After
flashing off the pyridine content in flash chamber 123, the
relatively pure anthracene oil flowing in conduit 62 is passed in
heat exchange relationship successively through heat exchangers
113, 91, 76 and 60, and is then introduced into anthracene oil
surge vessel 10 for recycle.
EXAMPLE II
A batch of several thousand pounds of Oklahoma Stigler seam coal
having a volatile matter content of 25.8 weight percent, a fixed
carbon content of 63.0 weight percent, an ash content of 12.1
weight percent, and a particle size of -65 mesh was treated in
facilities not shown in the drawing with 3 times its weight of
catalytic cracker slurry oil. The slurry oil had an API gravity of
2.2.degree. and a boiling range of 700.degree.-900.degree.F., and
was contacted with the coal at a temperaturee of
700.degree.-740.degree. F. in the presence of hydrogen and at a
pressure of 1,500 p.s.i.g. for 1 hour. Under these conditions 87
weight percent of the coal was dissolved. Upon cooling and
depressurization, the mixture was filtered to remove the insoluble
ash mineral. A sample of the deashed coal remaining in solution
contained 31.8 weight percent of volatile matter, 1.08 weight
percent of ash, and 67.1 weight percent of fixed carbon.
The filtered solution is transferred to coal storage vessel 17 for
fractionating into a plurality of fractions. Five hundred pounds
per hour of deashed coal solution is withdrawn from vessel 17 via
conduit 8 by means of pump 7 which raises the pressure to 1,200
p.s.i.g., and the solution is then passed to heater 9 where the
temperature is raised to approximately 500.degree. F. The heated
solution is introduced into mixer 38 and admixed with 2,500 pounds
per hour of hexane introduced via conduit 41 from light solvent
surge vessel 39. The temperature of the hexane is adjusted by heat
exchanger 115 to give a composite temperature in mixer 38 of
480.degree. F.
The solution is passed from mixer 38 to deashing-fractionating
vessel 45 in which the hexane density is 0.42 g./cc. The heavy
fluid phase 49 settling in vessel 45 is withdrawn at a rate of 10
pounds per hour and consists of 5 pounds per hour of hexane, 1.5
pounds per hour of ash mineral, and 3.5 pounds per hour of coal
liquefaction product.
The light phase 50 in vessel 45, consisting of a solution of the
remaining coal liquefaction products in the mixed slurry oil and
hexane solvent, is withdrawn via conduit 59 and passed to heat
exchanger 60 where its temperature is raised to 505.degree. F. The
heated solution is then introduced into vessel 63 wherein the
hexane density is 0.39 g./cc. A heavy fluid phase separates in
vessel 63, and is withdrawn at the rate of 180 pounds per hour.
Upon flashing off the hexane solvent, 90 pounds per hour of heavy
coal liquefaction product is obtained having a softening point of
about 400.degree. F., about 50 weight percent of volatile matter,
less than 0.1 weight percent of ash, and about 50 weight percent of
fixed carbon. The light phase 65 remaining in vessel 63 is
withdrawn and passed successively through heat exchangers 76 and 91
and heater 93. The heated solution is then introduced into vessel
92, thus bypassing vessel 77. Vessel 92 is operated at a
temperature of 560.degree. F., a pressure of 1,175 p.s.i.g., and a
hexane density of 0.33 g./cc. A fluid heavy phase 94 consisting of
equal parts by weight of hexane and light coal liquefaction product
separates in the bottom of vessel 92 and is withdrawn therefrom at
the rate of 30 pounds per hour. Upon flashing off the hexane
solvent, the light coal liquefaction product is fluid at room
temperature, and has a volatile matter content of 75 weight
percent, an ash content of less than 0.1 weight percent, and a
fixed carbon content of 25 weight percent.
The mixed solvent phase 95 is withdrawn via conduit 103, passed
through heat exchanger 113 and heater 104, and then introduced into
solvent separating vessel 105. The vessel 105 is operated at a
temperature of 800.degree. F., a pressure of 1,150 p.s.i.g., and a
hexane solvent density of 0.18 g./cc. The slurry oil forms a heavy
fluid phase 106 containing some hexane which is withdrawn via
conduit 122, the hexane is flashed off in flash chamber 123, and
the slurry oil is passed through heat exchangers 113, 91, 76 and 60
in succession to transfer its heat to the countercurrently flowing
solution of coal liquefaction products. The cool slurry oil then
leaves the system for reuse in dissolving more coal. The hexane
phase 107 leaving the top of vessel 105 is also passed successively
through heat exchangers 113, 91, 76 and 60 to transfer its heat to
the countercurrently flowing solution of coal liquefaction
products. The hexane is then given a final cooling in heat
exchanger 115 and returned to vessel 39 for reuse.
EXAMPLE III
One thousand grams of the filtered slurry oil solution of Stigler
seam coal of example II is refiltered and introduced into a
pressure vessel along with 5,000 grams of benzene. The vessel is
maintained at a pressure of 1,000 p.s.i.g. and the temperature is
raised in increments. The initial temperature level is 550.degree.
F., at which the density of the benzene is 0.52 g./cc. A fluidlike
heavy phase forms and is withdrawn from the bottom of the vessel
which phase consists of one part by weight of benzene and one part
by weight of heavy coal liquefaction products and ash mineral.
The temperature is raised to 600.degree. F., at which temperature
the density of the benzene is 0.34 g./cc. A fluidlike heavy phase
forms and is withdrawn. Upon flashing off the benzene, this heavy
phase has a volatile matter content of 32.1 weight percent, an ash
content of less than 0.1 weight percent, and a fixed carbon content
of 67.9 weight percent.
The temperature is raised to 655.degree. F., at which temperature
the benzene density is 0.20 g./cc. The heavy fluidlike phase which
forms is withdrawn from the bottom of the vessel and the benzene is
flashed off. This product has a volatile matter content of 66.2
weight percent and a fixed carbon content of 33.4 weight
percent.
The temperature is raised to 705.degree. F., at which temperature
the density of benzene is 0.16 g./cc. The heavy fluidlike phase
which forms is withdrawn from the vessel and is freed of solvent.
This product has a volatile matter content of 79.2 weight percent
and a fixed carbon content of 20.3 weight percent.
The temperature is raised to 785.degree. F., to provide a benzene
density of 0.13 g./cc. The fluidlike heavy phase which forms is
withdrawn and desolvated. This product has a volatile matter
content of 93.1 weight percent, a negligible ash content, and a
fixed carbon content of 6.9 weight percent.
When desired, the various heavy organic coal liquefying solvents
disclosed on pages 26 and 27 of the specification may be
substituted for anthracene oil in example I and for slurry oil in
examples II and III to thereby obtain comparable results.
Similarly, the various light organic solvents disclosed on pages
27-30 of the specification may be substituted for pyridine in
example I, for hexane in example II, and for benzene in example III
to thereby obtain comparable results.
* * * * *