A method of fractionating a mixture containing high boiling carbonaceous material and normally solid mineral matter includes processing with a plurality of different supercritical solvents. The mixture is treated with a first solvent of high critical temperature and solvent capacity to extract a large fraction as solute. The solute is released as liquid from solvent and successively treated with other supercritical solvents of different critical values to extract fractions of differing properties. Fractionation can be supplemented by solute reflux over a temperature gradient, pressure let down in steps and extractions at varying temperature and pressure values.

BACKGROUND OF THE INVENTION 
This invention relates to a method of fractionating a mixture of high 
boiling carbonaceous material including normally solid carbonaceous 
material and mineral matter. In particular, supercritical and near 
supercritical fluids are used in extraction and fractionation of the 
materials. 
Recent developments in the processing of fossil fuels have resulted in 
products and residua of extremely complex and intractable nature. This is 
especially true of the residua generated during coal liquefaction and 
various other processes involving heavy petroleum fractions, tarsands, 
shales, etc. Often such residua decompose prior to boiling and cannot be 
fractionated by conventional distillation processes. 
In other developments, supercritical fluids have been used for extracting 
and fractionating organic substances. Representative of these developments 
are U.S. Pat. No. 3,969,196 to Zosel; U.S. Pat. No. 4,354,922 to 
Derbyshire et al.; U.S. Pat. No. 4,482,453 to Commes et al. and U.S. Pat. 
No. 4,502,944 to Nelson. These prior developments involve multi-step 
procedures in which process conditions of a supercritical fluid are varied 
to extract and separate product fractions. Even with this existing 
technology, there remains a need for improvements in separating and 
fractionating intractable, carbonaceous residua that also include solid 
mineral matter. 
It is known that certain gas phases maintained near to supercritical 
conditions are capable of taking up large amounts of solutes from liquid 
or solid materials. When conditions such as temperature or pressure are 
reduced to below critical, a substantial decrease in solubility results. 
Also increases, particularly in temperature, to well above critical 
likewise reduce solubility in the supercritical gas. For purposes of this 
application, the terms "supercritical solvent", "supercritical phase", or 
"supercritical fluid" refer to a gas or gas mixture possibly with solute 
at or above critical temperature and critical pressure. The use of 
supercritical fluids to fractionate substances in a manner analogous to 
fractional distillation is termed "fractional destraction" in this 
application. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide an improved 
method of fractionating heavy, carbonaceous material including normally 
solid mineral matter. 
It is a further object to provide a method of separating high boiling 
carbonaceous residua from solid mineral matter with minimal loss of 
carbonaceous material. 
It is also an object to provide a method of fractionating high boiling 
residua at temperature and pressures below the boiling or decomposition 
conditions of the residua fractions. 
In accordance with the present invention, a method is provided for 
fractionating a mixture containing high boiling carbonaceous material and 
normally solid mineral matter. The method includes contacting the mixture 
in mass-transfer relation with a first supercritical solvent at 
temperature and pressure above the critical values for the solvent but 
below vaporization temperature of the mixture. A major fraction of the 
carbonaceous material is extracted as a first solute into the first 
solvent from the normally solid mineral matter. The first solute is 
released as liquid from supercritical phase leaving the solvent in gas 
phase. After separating from the gas, the released liquid is contacted 
with a second solvent at above critical values to extract a second solute 
fraction into supercritical phase. The second solvent has a critical 
temperature less than that of the first solvent. The second solute is 
released from the supercritical phase to form a second released liquid of 
higher average volatility than the first released liquid. 
In other aspects of the invention, third and successive solvents at 
supercritical conditions contact the second and successive residual 
liquids to extract a series of successive solutes into supercritical 
phase. The solutes are separately released from supercritical phase to 
provide a succession of liquids exhibiting a direct or inverse progression 
of properties such as volatility, average molecular weight, hydrogen to 
carbon ratio and solubility. Where the selected solvents have an upward 
progression of critical temperatures and an upward progression of 
operation temperatures from the second to the final contacting stages, the 
released liquids can be expected to have a progression of decreasing 
volatility. 
In yet other aspects of the invention, the mixture of high boiling 
carbonaceous material and solid mineral matter exhibits atmospheric 
boiling points or decomposition temperatures above 300.degree. C. 
In yet other aspects of the invention, the mixture of normally solid 
mineral matter and carbonaceous material includes a high boiling fraction 
from a coal liqufaction process. Each of the solvents selected for use 
have critical temperatures below the boiling temperatures of a major 
portion of the carbonaceous material in the mixture. Typically, solvents 
with critical temperatures of between 200.degree. and 400.degree. C. are 
selected. 
In other aspects of the invention, the solute is successively released from 
the supercritical solvent in a series of steps to provide a plurality of 
separate liquid fractions of different solubilities. The stepwise release 
can be accomplished by successive depressurization steps or by successive 
increases in temperatures. In a continuous fractionation process, the 
second solvent with solute in supercritical phase is continuously 
contacted with a reflux solute at temperatures from about 70.degree. C. 
above the critical temperature down to or near the critical temperature of 
the solvent. 
One other manner of fractionating the second solute is to contact the 
released liquid from a previous stage with a supercritical solvent in a 
progression of increasing pressure steps. This extracts a series of solute 
fractions having decreasing solubilities. These solute fractions are 
subsequently released from solvent by reducing the pressure of each 
fraction to below the critical pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In carrying out the method of the present invention, a residual material, 
such as a high boiling residuum from a coal liquefaction process is 
contacted in a series of steps with a plurality of different solvents at 
above critical values. The residuum may contain both solid mineral matter 
and very high boiling, difficult to dissolve, carbonaceous material of 
organic origin. 
In FIG. 1, a multiple solvent, fractional destraction process is 
illustrated for providing a plurality of liquid fractions from an 
intractable residual material. Residuum 11 enters an extractor 13 where it 
is contacted with a first supercritical solvent 15 at temperatures and 
pressures above the critical values of the solvent. Extractor 13 can be of 
various types of known liquid-gas, liquid-liquid or gas-liquid-solid 
contacting equipment. For example, a vessel or column containing a sparger 
or other means for distributing the supercritical solvent into a 
liquid-solid residuum can be used. 
Carbonaceous solute from residuum 11 is extracted into the supercritical 
solvent 15 and is withdrawn from extractor 13 at conduit 17. The residual 
solids 19 are removed for further processing or disposal. The 
supercritical solvent, pregnant with solute in conduit 17 is subjected to 
pressure reduction in vessel 21 to below the critical pressure of the 
solvent. The pressure reduction results in a released carbonaceous liquid 
at 23 and a solvent gas flow at 25. The solvent gas is recompressed in 
compressor 27 and recycled with temperature adjustments to extractor 13. 
In the extraction step at 13 and in subsequent contacting operations, the 
supercritical solvent is maintained at a temperature above but near to its 
critical temperature. Typically, no more than 50.degree.-70.degree. C. 
above the critical temperature is employed. In the initial extraction at 
13, the supercritical solvent is maintained as near as possible to the 
critical temperature to maximize the take up of solute. For example, a 
temperature of about 1.02 of the absolute critical temperature (Tc) will 
assure the presence of a supercritical phase but yet take full advantage 
of enhanced solubility near the critical temperature. 
As illustrated, the released liquid at 23 is passed to a fractional 
destraction column 29 for further fractionation with a second 
supercritical solvent 31. Typically, column 29 will include a lower 
portion 33 for introducting released carbonaceous liquid 23 and the second 
supercritical solvent 31. Solvent 31 advantageously is introduced through 
a sparger or some other suitable dispersion device into a level of 
carbonaceous liquid. 
The residual liquid that is not taken up by the supercritical solvent is 
withdrawn at 34. This liquid fraction will be of low solubility, hydrogen 
to carbon ratio, and volatility relative to the other fractions withdrawn 
from the upper portion 35 of column 29. 
The upper portion 35 of column 29 can include an inert packing for 
providing contact sites between the reflux liquid and supercritical 
solvent. It will be clear that sieve or bubble cap trays used in 
distillation processes and other gas-liquid or liquid-liquid contacting 
devices also can be used. 
Reflux of solute within column 29 is provided by a heater means 37, 
illustrated as a coil for passage of steam at the top of column 29. On 
increasing the temperature of the supercritical solvent at the top of 
column 29 to temperatures up to not more than about 70.degree. C. above 
the critical temperature will release a fraction of solute as reflux 
liquid within the column. As the reflux liquid flows downwardly in contact 
with upwardly flowing supercritical solvent, a continuous exchange of 
solute between liquid and supercritical phase occurs in accord with a 
temperature gradient established between the upper and lower portions of 
column 29. Consequently, a plurality of product fractions 39 can be 
withdrawn along the height of column 29. Fractions 39 can be withdrawn as 
supercritical solvent or as released liquid solute but if withdrawn as 
supercritical solvent, pressure let-down chambers 41 are used to separate 
the liquid solute from the supercritical solvent. 
The supercritical solvent leaving column 29 at 43 will contain a highly 
soluble and volatile liquid solute. On reducing the pressure to below 
critical in chamber 45, the volatile solute is released and withdrawn at 
51 as a premium, ash-free product. The solvent gas 47 at below critical 
conditions is recompressed in compressor 49 with temperature adjustments 
(not illustrated) and recycled at 31 into the lower portion of column 29. 
Gases 42 from Chambers 41 also can be recompressed and recycled as 
supercritical solvent. 
EXAMPLE 1 
In a process to simulate the FIG. 1 embodiment, a coal derived residuum 
containing solids is contacted with toluene at a temperature of 1.02 times 
the absolute critical temperature and a pressure of twice the critical 
pressure. About 70% of the residuum is extracted into the supercritical 
toluene and released on pressure reduction to below the critical pressure. 
The released solute with minimal ash content is then fractionated with 
cyclohexane in a fractional destraction device. Four overhead fractions 
are collected at 320.degree. C., 305.degree. C., 300.degree. C., and 
290.degree. C. These overhead fractions amount to about 40% of the 
original residuum feed. The residual carbonaceous liquid that is not taken 
up by the supercritical cyclohexane and the solids rich fraction from the 
toluene extraction each amount to for about 30% of the feed residuum. 
Table 1 below gives analyses of various fractions collected in a series of 
batch operations. This data is presented as potential performance of the 
process of this example. The average molecular weights (Mn) are taken from 
vapor pressure osmometry (VPO) data. 
TABLE 1 
__________________________________________________________________________ 
Elements (wt %) 
C H O N S H/C 
--M.sub.n (VPO) 
Ash (wt %) 
__________________________________________________________________________ 
Feed Residuum 
78.6 
5.3 
(5.2)+ 
1.1 
(1.1)+ 
0.809 
-- 13.2 
Cyclohexane 
Overheads: 
#1 (593 K)* 
88.2 
6.9 
2.8 0.9 
0.3 0.928 
388 &lt;0.1 
#2 (578 K)* 
88.9 
6.7 
3.3 0.9 
0.3 0.901 
443 &lt;0.1 
#3 (573 K)* 
89.0 
6.4 
3.2 1.0 
0.3 0.866 
525 &lt;0.1 
#4 (563 K)* 
89.6 
6.0 
3.1 1.2 
0.3 0.807 
578 &lt;0.1 
Cyclohexane 
89.6 
5.3 
3.5 1.4 
0.2 0.713 
1070 &lt;0.1 
Residue 
Toluene 44.8 
2.6 
(12.7)+ 
0.7 
(4.6)+ 
0.718 
-- 46.1 
Residue 
__________________________________________________________________________ 
*Reflux Zone Temperature 
+ Includes Mineral Matter Contributions 
It is clearly seen that only minimal ash is carried into the overhead 
product or to the residual carbonaceous liquid from the cyclohexane 
extraction. Furthermore, fractions with increased hydrogen to carbon 
ratios and lower average molecular weight are obtained in the fractions 
collected at elevated overhead temperatures. Also, one may expect an 
inverse relation of molecular weight to product volatility. 
It is also seen that the released solute from the toluene extraction can be 
regarded as the combination of the cylcohexane residue and the four 
overhead fractions. It is clear that this first released solute is of 
greater average molecular weight, lower hydrogen to carbon ratio and lower 
volatility than subsequent fractions. 
Various solvents can be selected for use as supercritical solvents in the 
process of this invention. The solvents are selected by their chemical and 
physical compatability with the materials to be fractionated. In addition, 
the solubility of the residuum in the solvent as well as the solvent in 
the solute fractions is considered. Moreover, the critical temperature and 
critical pressure of the solvent are of particular importance as they 
dictate the operating conditions of the process. The solvents preferably 
have critical temperatures below the vaporization and decomposition 
temperatures of the expected fractions to be recovered at the critical 
pressure of the solvent. This permits the critical and operating 
temperatures to be below the boiling and decomposition temperatures of the 
fractions at the operating pressure of the method. 
Solvent mixtures can be prepared to provide desired critical conditions and 
other physical and chemical properties of a desired solvent. Table 2 below 
lists the critical constants for a number of solvents contemplated for use 
either alone or in mixture with other solvents, in carrying out the 
present invention. 
TABLE 2 
______________________________________ 
Critical Constants 
Solvent Tc .degree. K. 
Pc Atm 
______________________________________ 
Carbon Dioxide 304 75 
Butane 425 37 
Methylpropane 408 36.5 
N--Pentane 470 33.1 
2 Methylbutane 461 32.9 
2-2-Dimethylpropane 
433 32.3 
Hexane 508 29.9 
2 Methylpentane 498 29.9 
3 Methylpentane 505 30.8 
2,2-Dimethylbutane 
489 30.7 
2,3-Dimethylbutane 
500 31 
Methanol 512 79.2 
Cyclohexane 553 40.1 
Benzene 562 49 
Toluene 593 41.7 
Pyridine 620 55.6 
______________________________________ 
Referring now to FIG. 2 where a more expanded form of the present process 
is illustrated. Residuum 61 is contacted with supercritical solvent 65 in 
extractor 63 with the removal of solids 69 and the pressure reduction of 
pregnant supercritical solvent 67 at 71. The released solvent gas 75 is 
recompressed at 77 with adjustments in temperature before returning to the 
extractor 63. The released liquid 73 is forwarded to a fractional 
destraction column 79 for contact and fractionation with a second 
supercritical solvent 81 and solute reflux provided by heater coil 87. As 
illustrated, released carbonaceous liquid 73 is fractionated into an 
overhead stream 93 and a residual liquid stream 83. It will be clear that 
several fractions can be taken from column 79 along its height as was 
illustrated and described in the FIG. 1 process. 
The pregnant supercritical solvent 93, following pressure reduction in 
vessel 95, separates into carbonaceous liquid 85 and recycle solvent gas 
97 for recompression in compressor 99, temperature adjustment and recyle 
into the lower portion of destraction column 79. 
The heavy liquid fraction 83 is passed on to a second destraction column 
109 for further fractionated with a third supercritical solvent 101. As 
previously described, heater coil 107 provides a liquid reflux for 
fractionating the solute into a plurality of fractions illustrated as the 
pregnant supercritical solvent 113, the residual carbonaceous liquid 103 
and the intermediate fraction 120. Pressure reduction at 115 and 122 
permit recycle of the solvent gases 117 and 123 for recompression at 119 
and return to column 109. Thus intermediate 121 and high volatile 105 
fractions of carbonaceous liquid are recovered. 
The use of this method as thus described permits much flexibility in the 
fractionation of an intractable residual material. Solid material is 
removed in an early step to prevent fouling of the later fractionating 
stages. Through use of the plurality of supercritical solvents, 
fractionation can occur at temperatures well below the boiling temperature 
at the collection pressure. The process is well suited for separating 
carbonaceous fractions that decompose before boiling and therefore cannot 
be separated by distillation processes. 
Advantageously, the first supercritical solvent is selected to have a high 
critical temperature and high solubility for taking up a large fraction of 
the carbonaceous material in the residuum. Following the release of the 
solute liquid from supercritical phase, subsequent processing with other 
supercritical solvents can be carried out to fractionate the released 
liquid. The second and subsequent supercritical solvents are 
advantageously selected to have critical temperatures in upward 
progression. This permits early recovery at low operating temperatures of 
the more soluble and volatile materials. Subsequent fractional destraction 
with third and successive supercritical solvents can employ progressively 
higher operating temperatures with solvents of increasing critical 
temperatures up to that of the initial extraction step. Furthermore, 
particular solvents can be selected to be directed to the extraction of 
particularly intractable fractions. Such flexibility previously has not 
been realized in distillation or single-solvent supercritical processing. 
EXAMPLE 2 
A coal derived residuum is extracted with toluene, n-pentane and 
cyclohexane to simulate the process of FIG. 2. Temperatures of about 
1.02-1.1 times the absolute critical temperature and pressures of about 2 
times the critical pressure were used in the extraction and fractional 
destraction operation. About 70% by weight of the feed residuum is 
extracted into supercritical toluene. After release from supercritical 
phase about 40% by weight of the released liquid is extracted into 
supercritical n-pentane and recovered as a light product fraction. The 
residual liquid from the n-pentane is passed to a second fractional 
destraction operation where supercritical cyclohexane is used to 
fractionate that residual liquid into extracted fractions of about 25% and 
45% and a cyclohexane residuum of about 30% by weight. 
In FIG. 3 a plurality of extraction steps 131 and 133 are performed as 
previously described except that the residual carbonaceous liquid 135 
after the second extraction is available as a product fraction. This is 
achieved by passing forward the released solute liquid 137 to subsequent 
extraction or destraction steps as illustrated at 139 with a third 
supercritical solvent 144. In a final fractional destraction step, a 
plurality of product fractions 141 and 143 along with a residual 
carbonaceous liquid 145 can be recovered as described above. 
This process variation gives additional flexibility in employing a 
plurality of supercritical solvents in the fractionation of the high 
boiling residual material. Early recovery of the high boiling, high 
molecular weight material can be obtained. Solvents with progressively 
decreasing critical temperatures are selected to provide fractions of 
progressively increasing volatility and solubility or of progressively 
decreasing molecular weight. 
Although fractional destraction has been described in the above method as 
involving a continuous process with temperature activated reflux, it will 
be clear that other techniques may be used. Batch and batch stage contact 
with supercritical solvent and refluxed solute can be used. Also, 
fractionation can be obtained by contacting the residual or released 
liquids with a second supercritical solvent in a progression of steps each 
with increased pressure. For instance, pressures of 1.0 to about 4 times 
supercritical pressures in three to five steps can provide a plurality of 
solute fractions of varying solubility or volatility. Similarly, residual 
material can be contacted with a second supercritical solvent in a 
plurality of temperature decreasing stages to extract a series of solute 
fractions of varying properties. 
It is therefore seen that the present invention provides a method of 
fractionation heavy, intractable, carbonaceous material that includes 
normally solid mineral matter. Solid mineral matter is removed in a first 
extraction with a supercritical solvent. In subsequent extraction and 
fractional destraction steps involving other solvents, the initial solute 
can be divided into a plurality of fractions. All of the extractions and 
fractionations can be performed at temperatures well below boiling or 
decomposition temperatures of the carbonaceous material through use of a 
plurality of carefully selected supercritical solvents. 
Although the present invention is described in terms of the specific 
embodiments, it will be clear that various changes in the materials, 
processing conditions, parts and details of the invention can be made by 
one skilled in the art within the scope of the appended claims.