Coal processing system for producing a stream of flowable insoluble coal products

An improved coal processing system wherein a feed mixture (including coal, dissolving solvent, insoluble coal products and soluble coal products) at a first temperature level is separated in a first separation zone into a heavy fraction including the insoluble coal products and a light fraction and, thereafter, the heavy fraction is withdrawn from the first separation zone and heated to a second temperature level higher than the first temperature level and in which the second temperature level is sufficiently high to produce a heavy fraction that is flowable.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the liquefaction and 
fractionation of hydrocarbonaceous materials and, more particularly, but 
not by way of limitation, to an improved system for producing a flowable, 
insoluble coal fraction. 
2. Description of the Prior Art 
Various coal processing systems have been developed in the past wherein 
coal has been treated with one or more solvents and processed to separate 
the resulting insoluble coal products from the soluble coal products, some 
systems including provisions for recovering the solvents. 
U.S. Pat. Nos. 3,607,716 and 3,607,717, issued to Roach and assigned to the 
same assignee as the present invention, disclose processes wherein coal is 
contacted with a solvent and the resulting mixture then is separated into 
a heavy phase containing the insoluble coal products and a light phase 
containing the soluble coal products. In such processes, the light phase 
is withdrawn and passed to downstream fractionating vessels wherein the 
soluble coal product is separated into multiple fractions. Other processes 
for separating the soluble coal products from the insoluble coal products 
utilizing one or more solvents are disclosed in U.S. Pat. No. 3,607,718, 
and 3,642,608, both issued to Roach et al., and assigned to the same 
assignee as the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing (FIGS. 1A and 1B), general reference numeral 
10 designates a coal processing system arranged in accordance with the 
present invention and generally including a first system 12 and a second 
system 14. In general, coal to be processed in accordance with this 
invention is contacted with a dissolving solvent and processed through the 
first system 12 to provide a feed mixture comprising the dissolving 
solvent, insoluble coal products and soluble coal products. 
The term "insoluble coal products" as used herein refers to the undissolved 
coal, ash, other solid inorganic particulate matter and other such matter 
which is insoluble in the dissolving solvent. 
The feed mixture is passed from the first system 12 to the second system 14 
via a conduit 16 wherein the feed mixture is separated in a first 
separation zone 18 at a first temperature level into a first heavy 
fraction comprising substantially the insoluble coal products and a first 
light fraction comprising substantially the soluble coal products and the 
dissolving solvent. The first heavy fraction is withdrawn from the first 
separation zone 18 through a conduit 20 and passed through a heater 22 
wherein it is heated to a second temperature level higher than the first 
temperature level, the second temperature level being sufficiently high to 
produce a flowable first heavy fraction which is withdrawn from the first 
separation zone 18 and which is capable of being passed downstream from 
the heater 22 via a conduit 24 in a more efficient and more economical 
manner than possible heretofore. 
The yield of soluble coal products is influenced by the first temperature 
level, i.e. the temperature level within the first separation zone 18. 
Thus, as the first temperature level is increased, the solubility of the 
soluble coal products reduces thereby reducing the yield of the desired 
soluble coal products. Therefore, it is desirable to maintain the first 
temperature level as low as feasible to obtain the greatest yield of the 
desirable soluble coal products in the overhead first light fraction 
within the first separation zone 18; however, it has been discovered that 
the viscosity of the first heavy fraction to be withdrawn from the first 
separation zone 18 increases to a level wherein the flowability of that 
first heavy fraction is substantially reduced and, in many systems, the 
flowability of the first heavy fraction is reduced to such a level that 
the first heavy fraction cannot be passed downstream from the first 
separation zone 18 in an efficient manner. Moreover, in many instances, 
the high viscosity of the heavy fraction tends to foul or clog the conduit 
20 and the downstream apparatus. 
Thus, it will be appreciated that a conflict exists between selecting a 
relatively low first temperature level in the first separation zone 18 to 
permit the highest possible yield of the desired soluble coal products and 
maintaining the temperature level of the first heavy fraction sufficiently 
high to produce a first heavy fraction which is flowable to decrease 
substantially the possibilities of fouling or clogging of downstream 
apparatus. 
The first heavy fraction withdrawn from the first separation zone 18 will 
contain some amount of the dissolving solvent. The conflict between the 
first temperature level and the desirable temperature level of the first 
heavy fraction withdrawn from the first separation zone 18, to maintain 
the withdrawn first heavy fraction in a flowable condition, is aggravated 
by the inherent characteristics of the dissolving solvent to flash out of 
the withdrawn first heavy fraction as the pressure on the withdrawn first 
heavy fraction is reduced, since the flashing of the dissolving solvent 
results in a reduction of the temperature level of the withdrawn first 
heavy fraction. 
In one aspect, the present invention resolves the conflicts and problems 
generally described above by establishing the first temperature level of 
the feed mixture in the first separation zone 18 at a level for optimizing 
the yield of the soluble coal products in the first light fraction 
followed by heating the first heavy fraction withdrawn from the first 
separation zone 18 in the heater 22 to a second temperature level which is 
higher than the first temperature level and sufficiently high to produce a 
flowable first heavy fraction, which is discharged from the heater 22 and 
passed into the conduit 24 to the downstream apparatus. 
Referring more particularly to the first system 12, a first dissolving 
solvent is passed from a first solvent surge vessel 26 through a conduit 
28 and into a mixer 30 at a rate of flow controlled by a valve 32 
interposed in the conduit 28. Make-up first dissolving solvent is supplied 
to the first solvent surge vessel 26 through a conduit 34 when a valve 36, 
interposed in the conduit 34, is opened. 
Pulverized coal is contained in a coal storage vessel 38 and is passed into 
the mixer 30 through a conduit 40 at a rate controlled by a solids feeder 
42 interposed in the conduit 40. The feed rates of the first dissolving 
solvent and the pulverized coal preferably are controlled to maintain the 
weight ratio of the first dissolving solvent to coal in the mixer 30 
within a range between about one-to-one and about twenty-to-one. More 
particularly, it has been found desirable to maintain the weight ratio of 
first dissolving solvent to coal in the mixer 30 in a range between about 
two-to-one and about five-to-one; best results have been obtained when the 
weight ratio was maintained at about three-to-one. 
In mixer 30, the coal and the first dissolving solvent are agitated with a 
stirring mechanism 44 at about ambient temperature and pressure to form a 
slurry. That slurry is withdrawn from mixer 30 through a conduit 46 by a 
pump 48, the slurry being discharged from the pump 48 through a conduit 50 
to a heater 52 where the slurry is heated in a coil 54. In one preferred 
form, gaseous hydrogen is passed from a source (not shown) through a 
conduit 56 connected to the conduit 50, the gaseous hydrogen is mixed with 
the slurry flowing through the conduit 50 and the resulting mixture is 
heated via the heater 52. A valve 58 is interposed in the conduit 56 and 
thus the gaseous hydrogen is mixed with the slurry flowing through the 
conduit 50 when the valve 58 is opened. 
The slurry in the conduit 50, which may include the gaseous hydrogen, is 
discharged from the heater 52 and passed through a conduit 60 into a 
liquefier 62. In one embodiment, the pressure level in liquefier 62 
(sometimes referred to herein as the "liquefaction pressure") is greater 
than about 1000 psig and preferrably in the range of about 1200 psig to 
about 1500 psig. The temperature level of the slurry in the liquefier 62 
(sometimes referred to herein as the "liquefaction temperature level") is 
determined by the temperature level of the slurry in the conduit 60, which 
is passed into the liquefier 62, and the temperature level of the heating 
medium (gas or fluid) passed through a conduit 64 and through a heating 
coil 66 disposed within the liquefier 62, the rate of flow of the heating 
medium being controlled via a valve 68 interposed in the conduit 64. In 
the operational embodiment mentioned before, the temperature level in the 
liquefier 62 is about 800.degree. F. and thus the heater 52 is designed to 
elevate the temperature level of the slurry passing therethrough to an 
elevated temperature level which preferably approximates the temperature 
level of the slurry in the liquefier 62, for example, about 800.degree. F. 
In the liquefier 62, the first dissolving solvent is contacted with the 
coal at the elevated liquefaction temperature and pressure for a period of 
time sufficient to solubilize the soluble constituents of the coal and 
produce a mixture of coal liquefaction products (the soluble coal 
products), the dissolving solvent and the insoluble coal products. The 
insoluble coal products consist largely of carbon and the ash mineral 
fraction of the coal. 
The mixture of soluble coal products, insoluble coal products, first 
dissolving solvent and gases is withdrawn from the liquefier 62 and passed 
through a conduit 70 into a degassing vessel 72 wherein the mixture is 
degassed by permitting the excess hydrogen, other gases and vapors to be 
discharged from the degassing vessel 72 through a conduit 74, a pressure 
reducing valve 76 being interposed in the conduit 74. The pressure 
reducing valve 76 is utilized to control the pressure on the mixture 
within the degassing vessel 72. In some operational embodiments, the 
hydrogen containing gases are discharged through the conduit 74 and passed 
to a hydrogen recycle system for recovering such hydrogen. In this 
embodiment the temperature level of the mixture in the degassing vessel 72 
is about 800.degree. F. and the pressure level in the degassing vessel 72 
is in the range of about 1200 psig to about 1500 psig. 
The degassed mixture is discharged from the degassing vessel 72 through a 
conduit 78 and passed into a flash vessel 80, the rate of flow being 
controlled by a liquid level control type of valve 82 interposed in the 
conduit 78. In the operational embodiment referred to before, the pressure 
level in the flash vessel 80 is about one atmosphere or about 20 psig and 
the temperature level is in the range of about 500.degree. to about 
600.degree. F. In the flash vessel 80 a substantial portion of the light 
organics, such as propane, hexane, toluene or benzene, for example, are 
flashed-off and discharged from the flash vessel 80 through the conduit 
84, the light organics being recoverable in any suitable manner (not 
shown). 
The mixture consisting essentially of the first dissolving solvent, the 
insoluble coal products and the soluble coal products in the lower portion 
of the flash vessel 80 is withdrawn through a conduit 86 and passed 
through a heater 88 wherein the temperature level of the mixture is 
elevated, the heated mixture being discharged from the heater 88 and 
passed into a vacuum flash column 90 (the vacuum source not shown in the 
drawing) via a conduit 92. A valve 94 is interposed in the conduit 92. 
In the vacuum flash column 90, vapors, including those of the first 
dissolving solvent, are removed overhead and passed from the vacuum flash 
column 90 through a conduit 96 and a heat exchanger 98 wherein they are 
condensed. The condensed first dissolving solvent is returned to the first 
solvent surge vessel 26 via a conduit 100 (sometimes referred to herein as 
"the return first dissolving solvent"). The heater 88 essentially 
establishes the temperature level of the mixture in the vacuum flash 
column 90 at a level to control the amount of the first dissolving solvent 
passed from the vacuum flash column 90 through the conduit 100 as return 
first dissolving solvent. 
In the example referred to before, the heater 88 heats the mixture passing 
therethrough to a level such that the temperature level of the mixture in 
the vacuum flash column 90 is about 650.degree. F., the pressure level in 
the vacuum flash column 90 being about 2 psia. The temperature level of 
the vapors passing through the conduit 96 is about 600.degree. F., the 
vapor temperature drop resulting primarily from the flashing of the first 
dissolving solvent in the vacuum flash column 90, and the temperature 
level of the condensed return first dissolving solvent passing from the 
heat exchanger 98 through the conduit 100 is about 200.degree. F. 
The vacuum bottoms in the lower portion of the vacuum flash column 90 are 
withdrawn through a conduit 102 by a pump 104. The vacuum bottoms consist 
essentially of the soluble coal products, the insoluble coal products and 
some of the first dissolving solvent, a large portion of the first 
dissolving solvent being flashed-off in the vacuum flash column and 
recovered as the return first dissolving solvent. The pump 104 discharges 
the mixture through a conduit 106 into a mixer 108 (sometimes referred 
herein as the "second mixer" and designated in the drawing via the symbol 
"M"). The temperature level of the mixture passing through the conduit 106 
is about 600.degree. F. and the pressure level is about 800 psig. 
In the embodiment of the invention shown in the drawing, a second 
dissolving solvent is contained in a second solvent surge vessel 110. The 
second dissolving solvent is withdrawn from the vessel 110 through a 
conduit 112 and pumped by a pump 114 through a conduit 116 into the mixer 
108. Make-up second dissolving solvent is added to the second solvent 
surge vessel 110 via conduit 118 and the flow of the make-up second 
dissolving solvent is controlled by a valve 120 interposed in the conduit 
118. In the mixer 108, the mixture discharged from the conduit 106 is 
contacted by the second dissolving solvent discharged from the conduit 116 
and the resulting mixture is discharged from the mixer 108 into and 
through the conduit 16, the mixture discharged from the mixer 108 
comprising and being referred to herein as the "feed mixture" and being at 
a temperature level of about 630.degree. F. 
Thus, the embodiment shown in the drawing contemplates the utilization of 
two, different dissolving solvents, one of the dissolving solvents being 
introduced from the first solvent surge vessel 26 and sometimes referred 
to herein as the "first dissolving solvent", and one other dissolving 
solvent being introduced from the second solvent surge vessel 110 and 
sometimes referred to herein as the "second dissolving solvent". However, 
the present invention also contemplates systems wherein the coal is 
contacted by a single dissolving solvent or systems wherein the coal is 
contacted by more than two dissolving solvents. Therefore, the feed 
mixture passing through the conduit 16 and introduced into the first 
separation zone 18 is referred to herein as including the dissolving 
solvent, which may be second dissolving solvent or the first dissolving 
solvent or a combination of the first and the second dissolving solvents 
or some other dissolving solvent or solvents utilized in a system (not 
shown in the drawing) for producing the feed mixture, unless the 
dissolving solvent is particularly designated as the "first dissolving 
solvent" or the "second dissolving solvent". 
Referring now more particularly to the second system 14, the first 
separation zone 18 comprises a first phase separating vessel 122 and, in 
the vessel 122, the feed mixture is separated to form the first light 
fraction in a upper portion 124 of the vessel 122 and the first heavy 
fraction in a lower portion 126 of the vessel 122, the first heavy 
fraction being allowed to settle within the lower portion 126 while the 
first light phase rises to the upper portion 124. In the particular 
embodiment referred to before, the temperature level in the first 
separation zone 18 (the first temperature level) is lower than about 
680.degree. F. and, more particularly, the first temperature level is 
about 630.degree. F. The pressure level in the first separation zone 18 is 
higher than about 600 psig and in a range of about 600 psig to about 1500 
psig. More particularly, the pressure level in the first separation zone 
18 is about 800 psig. 
The first heavy fraction is withdrawn from the first phase separating 
vessel 122 and passed through the heater 22 wherein the first heavy 
fraction is heated to the second temperature level. More particularly, the 
first heavy fraction is passed through a coil 128 in the heater 22 and a 
heating medium (a gas or a fluid) is passed through a conduit 130 in heat 
exchange relationship with respect to the first heavy fraction passing 
through the coil 128 to thereby elevate the temperature level of the first 
heavy fraction to the second temperature level. The heated first heavy 
fraction is discharged from the heater 22 into the conduit 24 and, at this 
stage in the process, the mixture in the conduit 24 is essentially a two 
phase system that is at a pressure level substantially equal to the 
pressure level of the first heavy fraction in the first separation zone 
18, namely about 800 psig. 
The heated first heavy fraction is passed from the heater 22 through the 
conduit 24 and into a second phase separating vessel 132 wherein the first 
heavy fraction is allowed to separate within a second separation zone 134 
within the second phase separating vessel 132 to form a fluid-like second 
heavy fraction which accumulates in a lower portion 138 of the second 
phase separating vessel 134, and a second light fraction which rises to an 
upper portion 136. The second light fraction includes the dissolving 
solvent (primarily the second dissolving solvent in the embodiment shown 
in the drawing) and soluble coal products. This second light fraction is 
withdrawn from the second phase separating vessel 134 through a conduit 
140. 
The pressure level in the second separation zone 134 is slightly less than 
the pressure level in the first separation zone 18 and, more particularly, 
the pressure level in the second separation zone 134 is in the range of 
about 590 psig to about 1490 psig. The temperature level in the second 
separation zone 134 is about the same as the second temperature level, 
that is, about the same as the temperature level of the first heavy 
fraction which is discharged from the heater 22. 
The second heavy fraction is withdrawn from the second phase separating 
vessel 132 through a conduit 142 at a flow rate controlled by a level 
control valve 144 interposed in the conduit 142. The level control valve 
144 flashes the second heavy fraction to substantially atmospheric 
pressure, and a stream, which is essentially, a two phase system, passes 
from the level control valve 144 into a third phase separating vessel 146 
(diagrammatically shown in the drawing as a conventional cyclone separator 
type of separating vessel). The pressure level in the third phase 
separatint vessel 146 is lower or below the pressure level in the second 
separation zone 134 and the temperature level in the third phase 
separating vessel 146 is in the range of about 500.degree. to about 
600.degree. F. 
The flashed second heavy fraction is separated in a third separation zone 
147 formed in the third phase separating vessel 146 into an overhead third 
light solvent fraction and a bottom third heavy fraction. The overhead 
light solvent fraction rises to an upper portion 148 of the third phase 
separating vessel 146 and is withdrawn through a conduit 150, a valve 152 
being interposed in the conduit 150. The overhead third light solvent 
fraction may be condensed and returned to the second solvent surge vessel 
110, if desired. 
The third heavy fraction which accumulates in a lower portion 154 of the 
third phase separating vessel 146 is withdrawn through a conduit 156 by a 
pump 158 and is discharged through a conduit 160 to downstream apparatus 
(not shown). The third heavy fraction withdrawn from the third phase 
separating vessel 146 comprises substantially all of the suspended 
particles of insoluble coal products contained in the feed mixture 
initially fed to the first phase separating vessel 122 via the conduit 16. 
In the embodiment referred to before, the first heavy fraction is heated to 
the second temperature level of about 680.degree. F. by the heater 22 to 
produce the flowable first heavy fraction in the conduit 24 and, because 
of such heating: (1) the first heavy fraction is maintained in a flowable 
condition as it is passed into the second separation zone 134; (2) the 
second heavy fraction is in a flowable condition within the second 
separation zone 134 (the pressure level in the second separation zone 134 
being substantially the same as the pressure level in the first separation 
zone 18, namely about 800 psig); (3) the second heavy fraction also is 
flowable as it is flashed through the valve 144 and passed to the third 
separation zone 147; and (4) the third heavy fraction is flowable within 
the third separation zone 147 as it is withdrawn and pumped into the 
conduit 160. The temperature level of the second heavy fraction is reduced 
as a result of the flashing of the second heavy fraction in the valve 144 
and, in this embodiment, the temperature level within the third separation 
zone 147 and the temperature level of the third heavy fraction withdrawn 
from the third separation zone 147 are each in a range of about 
500.degree. to about 600.degree. F., the flowability of the third heavy 
fraction facilitating the pumping of the third heavy fraction by the pump 
160. 
In some applications, it may be desirable to withdraw the first heavy 
fraction from the conduit 24, thereby eliminating the separations 
accomplished within the second and the third phase separating vessels 132 
and 146. In such applications, the first heavy fraction is withdrawn 
through a conduit 172 by opening a valve 174, interposed in the conduit 
172. The conduit 172 can be connected directly to a pump (not shown) for 
pumping the first heavy fraction from the first phase separating vessel 
122. In other applications, it may be desirable to pass the first heavy 
fraction directly into the third phase separating vessel 146 and, in such 
applications, the conduit 172 is connected to the conduit 142, thereby 
by-passing the second phase separating vessel 132. 
In still other applications, it may be desirable to pump the second heavy 
fraction directly from the second phase separating vessel 132 and, in 
these applications, the second heavy fraction is withdrawn through a 
conduit 176 by opening a valve 178, interposed in the conduit 176. In this 
last-mentioned application, the conduit 176 can be connected to other 
downstream apparatus (not shown) or the conduit 176 can be connected to a 
pump (not shown) for pumping the second heavy fraction directly from the 
second phase separating vessel 132. 
Thus, the present invention contemplates producing a flowable first, second 
and third heavy fraction, in one aspect; in another aspect, the invention 
contemplates producing a flowable first and third heavy fraction; in yet 
another aspect, the invention contemplates producing only a flowable first 
heavy fraction; and, in still another aspect, the invention contemplates 
producing a flowable first and second heavy fraction. 
The first light fraction, which rises to the upper portion 124 of the first 
phase separating vessel 122, is a solvent-rich fraction comprising 
substantially the soluble coal products and the second dissolving solvent. 
The first light fraction is withdrawn from the first phase separating 
vessel 122 through a conduit 162 and passed through a heat exchanger 164 
interposed in the conduit 162, to fractionating equipment designated in 
the drawing by the general reference numberal 166, the second light 
fraction in the conduit 140 being combined with the first light fraction 
in the conduit 162. In one embodiment, the fractionating equipment 166 is 
designed to separate the first light fraction into one or more coal 
liquefaction fractions (soluble coal products) which are discharged 
through a conduit 168 (the conduit 168 being two or more separate conduits 
in those systems where the soluble coat products are separated into more 
than one fraction with each individual fraction passing through one of the 
several conduits represented by the conduit 168 diagrammatically shown in 
the drawing). 
The dissolving solvent passed into the fractionating equipment 166 via the 
conduit 162 is separated from the soluble coal products. The separated 
dissolving solvent is passed from the fractionating equipment 166 through 
a conduit 170, through the heat exchanger 164 and returned to the second 
solvent surge vessel 110 to thereby recover the dissolving solvent. The 
dissolving solvent returned to the second solvent surge vessel 110 from 
the fractionating equipment 166 sometimes is referred to herein as the 
"return second dissolving solvent" and substantially comprises the second 
dissolving solvent in the operational example shown in the drawing. 
In the embodiment of the present invention shown in the drawing, the first 
dissolving solvent preferably is an organic solvent suitable for 
liquifying coal in the manner herein described. Various solvents suitable 
for use as the first dissolving solvent are described in detail in U.S. 
Pat. Nos. 3,607,716, 3,607,717, 3,607,718, and 3,642,608. The second 
dissolving solvent is of the type sometimes described as a "light organic 
solvent" in the just mentioned patents and consists essentially of at 
least one substance having a critical temperature below 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 claim 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 containing from about 2-8 carbon 
atoms, carbocyclic amines having a monocyclic structure containing from 
about 6-9 carbon atoms, heterocyclic amines containing from about 5-9 
carbon atoms, and phenols containing from about 6-9 carbon atoms and their 
homologs. 
The term "flowable" as used herein to describe the condition of the heavy 
fraction (more particularly, the first heavy fraction or the second heavy 
fraction or the third heavy fraction depending on the particular stage in 
the system of the present invention) refers to the movability of the heavy 
fraction through a conduit wherein the heavy fraction is passed through 
such conduit via gravity, a pressure differential or other such similar 
means for passing streams through conduits or the like. In one more 
specific aspect, the term "flowability" refers to the viscosity of the 
heavy fraction and, in those applications wherein the first heavy fraction 
is withdrawn from the first separating zone 18 and heated to a second 
temperature level above about 630.degree. F. at a pressure level of about 
800 psig, the term "flowability" contemplates a heated first heavy 
fraction in the conduit 24 having a viscosity in the range of about 1000 
centipoise to about 50,000 centipoise, for example. Further, referring to 
this specific aspect, the term "flowability" contemplates a second heavy 
fraction in the conduit 142 having a viscosity in the range of about 1000 
centipoise to 50,000 centipoise, at a pressure level of about 800 psig and 
a temperature level of about 680.degree. F., and a third heavy fraction in 
the conduit 156 having a viscosity in the range of about 4000 centipoise 
to 200,000 centipoise at a pressure level of about one atmosphere and a 
temperature level of about 500.degree. F. to about 600.degree. F. (The 
viscosity of the third heavy fraction being above about 500 centipoise). 
It should be noted that the first heavy fraction may be heated in the first 
separation zone 18 before withdrawing the first heavy fraction, which may 
be desirable in some applications. In this particular embodiment, (not 
shown in the drawing), a heater is located within the first phase 
separating vessel 122 and, preferably, the heater is disposed near the 
outlet connection of the first phase separating vessel 122 for heating the 
first heavy fraction to the second temperature level immediately prior to 
withdrawing the first heavy fraction so the first temperature level in the 
first separation zone 18 is maintained lower than the second temperature 
level of the first heavy fraction to be withdrawn. 
The particular example referred to herein specifically contemplates benzene 
as the second dissolved solvent although the various temperature and 
pressure levels specifically identified herein are applicable generally to 
other similar dissolving solvents. 
Changes may be made in the process apparatus or in the steps of the process 
or in the sequence of the steps of the process of the present invention 
without departing from the spirit and scope of the invention as defined in 
the following claims.