Process for the liquefaction of coal and separation of solids from the product stream

Production of a low mineral content fuel by a coal liquefaction process utilizing a hydrogenated coal solvent having been hydrogenated to remove at least about 80% of the asphaltenes which yields as the primary product a mixture of liquid and solids, a part of which is suspended in the liquid. The suspended solids are effectively removed with minimum loss of desired product by means of a light aromatic solvent in combination with a hydrogenated coal solvent having been hydrogenated to remove at least about 80% of the asphaltenes.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the conversion of coal to a clean 
fuel, that is, a fuel which is substantially free of the mineral 
components normally found in coal. 
In particular, the invention relates to a coal liquefaction process wherein 
a hydrogenated coal solvent and hydrogen are present during the 
liquefaction of the coal. The primary product of the coal liquefaction 
process is a mixture of liquid and undissolved solids. Some gas is 
generally also produced. A portion of the undissolved solids appears as 
extremely finely divided particles of the order of ten microns or less in 
size. These particles are rich in mineral matter normally found in all 
coals. Combustion of fuel containing these particles forms ash. 
Complete separation of such finely divided particles from the liquid in 
which they are suspended cannot be accomplished by the usual mechanical 
separation techniques at ordinary temperatures, which techniques include 
filtration, centrifugation, and settling, because of the extremely fine 
state of subdivision of the solid particles and because of the high 
viscosity of the liquid. Separation is improved by operation at elevated 
temperatures due to a rapid decrease in liquid viscosity, as well as an 
increase in the density differential between liquid and solid. Even at 
these elevated temperatures and reduced viscosities, the conventional 
separation techniques may be only partially effective. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a novel process for the 
liquefaction of carbonaceous solids such as coal in order to produce 
valuable hydrocarbonaceous products. 
Another object of the present invention is to provide a process for the 
separation of finely divided particulate matter from coal extract. 
Yet another object of the present invention is to provide a process which 
retards the formation and growth of asphaltenes thereby permitting a 
higher recovery of valuable products. 
A particular object of the present invention is to provide a process for 
producing hydrocarbonaceous products from coal using a particular method 
for liquefying and recovering the coal extract in which the coal is 
liquefied with a hydrogenated coal solvent having been hydrogenated to 
remove at least about 80% of the asphaltenes in the presence of hydrogen 
and in which the finely divided particulate removal is enhanced by the 
presence of a light aromatic solvent and a hydrogenated coal solvent 
having been hydrogenated to remove at least about 80% of the asphaltenes. 
In an embodiment, the present invention relates to a process for producing 
hydrocarbonaceous liquid products from coal which comprises the steps of: 
(a) contacting the coal, at a temperature of from about 150.degree. to 
about 450.degree. C. and a pressure of from about 10 to about 300 
atmospheres with a hydrogenated coal oil solvent having been hydrogenated 
to remove at least about 80% of the asphaltenes; (b) separating gas from 
the resultant mixture to provide a liquid phase comprising coal extract, a 
hydrogen-depleted liquefaction zone effluent solvent and finely divided 
solid particles; (c) supplying said liquid phase including substantially 
all of said hydrogen-depleted liquefaction zone effluent solvent, to a 
pre-mix zone and therein commingling the same with from about 10 weight 
percent to about 1000 weight percent of a light aromatic solvent selected 
from the group consisting of benzene, toluene and xylene and with from 
about 0.1 weight percent to about 1000 weight percent of fresh 
hydrogenated coal oil solvent having been hydrogenated to remove at least 
about 80% of the asphaltenes at a temperature of from about 10.degree. C. 
to about 150.degree. C. and a pressure of from about atmospheric to about 
25 atmospheres; (d) introducing the mixture from the pre-mix zone to a 
separation zone and therein separating a solid ash from the admixed 
liquids; (e) thereafter removing said light aromatic solvent from said 
admixed liquids in a solvent recovery zone; (f) removing an ash-free 
hydrocarbon stream from said solvent recovery zone and hydrogenating at 
least a portion thereof to form a hydrogenated coal oil; and (g) supplying 
at least a portion of said hydrogenated coal oil to step (a) and (c) as 
said hydrogenated coal oil solvent. 
We have found that coal and other similar carbonaceous solids can be 
liquefied to produce valuable hydrocarbonaceous products by treating the 
coal with a hydrogenated coal solvent having been hydrogenated to remove 
at least about 80% of the asphaltenes and hydrogen, and then adding a 
light aromatic solvent and fresh hydrogenated coal oil solvent, having 
been hydrogenated to remove at least about 80% of the asphaltenes, before 
the separation of ash from the coal extract. Superior ash separation and 
the minimization of asphaltene formation thereby results from our 
invention. 
It is well known that raw coal liquefaction products contain what are 
commonly referred to as "asphaltenes." Traditionally asphaltenes have been 
defined as hydrogen-deficient high molecular weight hydrocarbonaceous 
materials which are insoluble in straight chain aliphatic hydrocarbons 
such as n-pentane or n-heptane. We now recognize that the broad term 
asphaltenes relates to a wide spectrum of hydrocarbonaceous materials 
which may be further characterized. A heptane insoluble asphaltene may be 
further extracted by using benzene, chloroform and DMF (dimethyl 
formamide) solvents in that order. The benzene soluble asphaltenes are 
characterized with a high proportion of molecules having a molecular 
weight in the range of from about 450 to about 650 and only mildly 
hydrogen-deficient. The chloroform soluble asphaltenes are characterized 
with a high proportion of molecules having a molecular weight in the range 
of from about 1000 to about 1200. The DMF soluble asphaltenes are 
characterized with a high proportion of molecules having a molecular 
weight in the range from about 1800 to about 2000 and are severely 
hydrogen deficient. In a typical coal liquefaction extract, the benzene, 
chloroform and DMF soluble asphaltene fractions would be expected to be 
about 50, 35 and 15 volume percent, respectively, of the heptane insoluble 
asphaltene fraction. 
Although the exact mechanism of the asphaltene conversion in a 
hydrogenation zone is not known for certain, we believe that the higher 
molecular weight asphaltenes (are converted to lower molecular weight 
asphaltenes) and that the original lower molecular weight asphaltenes are 
converted to distillates. This theory is the antithesis of any speculation 
that the higher molecular weight asphaltenes are converted directly to 
distillates. The least nocuous of these asphaltenes are the benzene 
soluble asphaltenes which may be satisfactorily processed in conventional 
downstream petroleum refining processes. The benzene soluble asphaltenes 
also have the least propensity to coke or to promote further growth of 
larger asphaltenes, have the highest hydrogen to hydrocarbon ratio and 
perform as the best coal liquefaction solvent as compared to any other 
types of asphaltenes. 
Therefore, when we refer to a hydrogenated coal solvent having been 
hydrogenated to remove at least about 80% of the asphaltenes we mean a 
solvent which has been hydrogenated to remove essentially all of the 
chloroform and DMF soluble asphaltenes while permitting the presence of a 
small percentage of the relatively innocuous benzene insoluble 
asphaltenes. We have discovered that the presence of up to about 3 weight 
percent of these lower molecular weight asphaltenes has no deleterious 
effect on the liquefaction, separation or downstream processing steps of 
the present invention. Typically, when at least about 80% of the 
alphaltenes are removed from a coal liquefaction extract via 
hydrogenation, less than about 3 weight percent of the hydrogenated coal 
oil solvent is benzene soluble asphaltenes with essentially no chloroform 
or DMF soluble asphaltenes present. 
The coal was pulverized to provide particles sufficiently small to pass 
through a 200 mesh Tyler screen. One hundred grams of the pulverized coal, 
200 grams of previously extracted hydrogenated coal oil solvent and 
hydrogen were admixed in a liquefaction zone at a pressure of 2500 psig., 
a temperature of 420.degree. C. (788.degree. F.), a solvent to coal ratio 
of 2:1 by weight, with a liquid hourly space velocity (LHSV) of 0.8.

Referring to the drawing, hydrogen is introduced into the operation via 
conduit 1 and passed into conduit 18 which contains a hydrogenated coal 
solvent having been hydrogenated to remove at least about 80% of the 
asphaltenes described hereinafter. Comminuted coal is passed into conduit 
18 via conduit 2. The coal is comminuted to sufficiently small size to 
pass through a 200 mesh Tyler sieve, or finer, before being passed into 
conduit 2. The coal, hydrogen and coal solvent are then passed via conduit 
18 into liquefaction zone 3. The coal is processed in liquefaction zone 3 
at a pressure of from about 1000 psig. to about 7000 psig., at a 
temperature of from about 350.degree. to about 500.degree. C., a space 
velocity of from about 0.2 to about 8, with a hydrogen circulation rate of 
from about 10,000 to about 300,000 standard cubic feet per ton of coal, 
and with a solvent to coal weight ratio of from about 1:1 to about 4:1. 
The treated mixture is passed out of liquefaction zone 3 through conduit 4 
into gas separator 5. In gas separator 5 unconsumed hydrogen and any other 
gases present are separated from the liquid and are passed out of gas 
separator 5 via conduit 6. The non-gaseous components are passed out of 
gas separator 5 via conduit 7 into premix zone 8. Makeup aromatic solvent 
is introduced to the operation via conduit 9 and is passed into conduit 
14, which contains a recycle aromatic solvent stream described 
hereinafter. Suitable low boiling range aromatic solvents are benzene, 
toluene, xylene, etc. The aromatic solvent is then intimately mixed with 
the above-mentioned non-gaseous components. Fresh hydrogenated coal oil 
solvent having been hydrogenated to remove at least 80% of the asphaltenes 
is introduced via conduits 18, 25 and 7. The fresh coal oil solvent is 
then mixed with the non-gaseous components in pre-mix zone 8. The mixture 
is passed out of pre-mix zone 8 via conduit 10 into separation zone 11. In 
separation zone 11, solid materials are removed by conventional means for 
removing solids from liquids, such as centrifugation, filtration, etc. The 
ash and any other solid materials, such as undissolved organic components 
of the coal, are withdrawn from separation zone 11 via conduit 23 and are 
passed out of the operation. The solid-free liquid is passed out of 
separation zone 11 via conduit 12 into solvent recovery zone 13 which 
consists of any suitable fractionator for fractionally distilling 
relatively high boiling liquids. The primary function of the fractionator 
is to recover aromatic solvent from the solid-free liquid. Recovered 
aromatic solvent is passed from solvent recovery zone 13 via conduit 14 
and recycled to pre-mix zone 8 for further use as described above. The 
desired low mineral content extract is passed from solvent recovery zone 
13 via conduit 15 into hydrogenation zone 16. In the hydrogenation zone, 
the clarified extract is contacted with hydrogen, introduced by means of 
conduit 24, and a suitable hydrogenation catalyst. Such catalysts are well 
known in the art and may contain nickel, molybdenum, cobalt, palladium, 
and tungsten on various porous inorganic supports, such as kieselguhr, 
alumina, silica, mordenite, faujasite, etc. 
The clarified extract may be processed upflow, downflow, or in a slurry. 
Hydrogenation is preferably in the liquid phase, but may be in the mixed 
phase or vapor phase. Preferably, the hydrogenation reaction performed in 
hydrogenation zone 16 occurs under hydrogenation conditions which include 
a temperature from about 600.degree. F. to about 900.degree. F. preferably 
about 725.degree. F., a pressure from about 1000 to about 5000 psig., a 
liquid hourly space velocity from about 0.5 to about 5, and a hydrogen 
circulation rate from about 3000 to about 10,000 S.C.F.B. 
The products of the hydrogenation zone are removed via conduit 17 and 
introduced into a fractionation zone 19, where the clarified hydrogenated 
products are fractionated into a plurality of various product streams 
which are removed via conduits 20, 21 and 22 for further conventional 
refining or for use as a fuel or petrochemical feed stock, as desired. 
Another hydrogenated coal oil stream having been hydrogenated to remove at 
least about 80% of the asphaltenes is passed from fractionation zone 19 
via conduit 18 for recycle to liquefaction zone 3 and pre-mix zone 8. 
DETAILED DESCRIPTION OF THE INVENTION 
The carbonaceous, solid materials which can be treated in the present 
process include any sort of coal, e.g., bituminous coal, lignite, 
sub-bituminous coal, etc. Other solid carbonaceous materials such as peat, 
oil shale, tar sand and the like may also be utilized, but may not 
necessarily give equivalent results. The preferred carbonaceous solid is a 
bituminous coal. For example, an Illinois Bellville district stoker coal 
having a moisture and ash free (MAF) volatile content of about 20% or 
higher is particularly suitable. Although not essential, it is preferred 
that the coal to be employed in the operation is first reduced to a 
particulate, comminuted form. Preferably, the coal is ground or pulverized 
to provide particles sufficiently small to pass through a 100 mesh Tyler 
sieve or smaller. Coal which is ground sufficiently fine to pass through a 
200 mesh Tyler sieve is particularly preferred for use. 
Liquefaction conditions employed in treating the solid coal in the 
liquefaction step include a temperature range from about 650.degree. to 
about 900.degree. F. and a pressure from about 500 psig. to about 5000 
psig. The hydrogen circulation rate may be fairly low, and may suitably 
range from about 1000 to about 20,000 S.C.F.B. of coal slurry charge. The 
solvent to coal weight ratio may suitably range from about 0.5:1 to about 
5:1 and the liquid hourly space velocity ranges from about 0.5 to about 5. 
The coal liquefaction step in the present process may be performed in a 
batch type operation or a continuous type operation. When a batch 
operation is employed, fixed amounts of the coal, hydrogen and coal oil 
solvent are charged to a suitable conventional coal liquefaction reactor, 
such as a rocking autoclave. The reactants are contacted in the 
liquefaction reactor for a period of time sufficient to produce the 
desired amount of conversion and then the mixture is withdrawn from the 
liquefaction zone. A suitable contact time in a batch type operation is 
from about 0.5 hour to about 3 hours, preferably, from about 1 hour to 
about 2 hours. In a continuous type operation, the coal, hydrogen and coal 
solvent are continuously charged to a suitable conversion zone which may 
be of any type known in the art, and the reactants are contacted therein. 
The resulting mixture is continuously withdrawn from the reactor. A liquid 
hourly space velocity (LHSV) in a continuous type operation (defined as 
volume of the reactor divided by the total volume of the reactants charged 
per hour) of about 0.5 to about 5 may be employed, and a LHSV of about 
0.6 to about 1.5 is particularly preferred. 
The liquefaction zone or reactor utilized in the solid coal conversion step 
of the present process may be any suitable vessel or reactor which can 
maintain the reactants at the desired temperature and pressure in order to 
provide the required liquefaction conditions. For example, a conventional 
rocking autoclave is a suitable reactor for use in a batch type process. A 
variety of vessels suitable for use in the solid coal conversion step in 
the present process are known in the art of coal liquefaction. Preferably, 
the conversion zone includes some means for admixing the reactants, such 
as by stirring or other agitation. 
The mixture recovered from the liquefaction zone includes hydrocarbonaceous 
material and ash. The hydrocarbonaceous phase recovered from the 
conversion step comprises a material which is generally liquid at room 
temperature and which has an ash content and a sulfur content 
significantly lower than the inorganic content and the sulfur content, 
respectively, of the untreated bituminous coal. One of the major drawbacks 
encountered in prior art coal liquefaction operations has been the 
difficulty of separating ash from the liquefied hydrocarbonaceous 
materials after liquefaction. By using a hydrogenated coal oil solvent 
having been hydrogenated to remove at least about 80% of the asphaltenes 
in the liquefaction step and by contacting the resulting hydrocarbonaceous 
extract, in the presence of the hydrogen-depleted coal oil solvent, with a 
low boiling range aromatic solvent and fresh hydrogenated coal oil solvent 
having been hydrogenated to remove at least about 80% of the asphaltenes, 
the present process significantly reduces the amount of asphaltenes 
present in the liquefied hydrocarbonaceous phase recovered in the 
separation zone, since the hydrogenated solvent tends to retard or inhibit 
the initial formation and growth of asphaltenic materials during the 
liquefaction step and the light aromatic solvent and the fresh 
hydrogenated coal oil solvent addition in a pre-mix zone unexpectedly 
promotes the separation of ash from the hydrocarbonaceous extract. 
The hydrocarbonaceous phase recovered by separating the ash from the 
mixture resulting from the solid coal conversion operation comprises a 
material which is generally liquid at room temperature when bituminous 
coal is used. This hydrocarbonaceous phase comprises a mixture of various 
hydrocarbonaceous compounds containing about 86-90 weight percent carbon 
and about 7-9 weight percent hydrogen. This recovered hydrocarbonaceous 
phase is further treated in a solvent recovery zone to recover the light 
aromatic solvent which may be recycled to the hereinabove mentioned 
pre-mix zone. A suitable solvent recovery zone may include a fractionation 
zone or any other technique for separating light aromatic hydrocarbons 
from coal liquefaction product. 
At least a portion of the low mineral content extract is hydrogenated to 
provide a valuable hydrocarbonaceous product and to supply the 
hydrogenated coal oil solvent having been hydrogenated to remove at least 
about 80% of the asphaltenes which is used in the initial liquefaction 
step and in the pre-mix zone. 
The following example is presented in illustration of the preferred 
embodiment and is not intended as an undue limitation on the generally 
broad scope of the invention as set out in the appended claims. 
EXAMPLE 
A seam coal from Randolph Co., Bellville District, Ill., was analyzed to 
determine its average composition, which was found to be as shown in Table 
I. 
TABLE I 
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Wt. % 
______________________________________ 
Ash 10.18 
Total Nitrogen 1.32 
Leco Sulfur 3.34 
Total Oxygen 9.54 
Free Water 4.00 
Volatiles 39.72 
Carbon 64.45 
Hydrogen 5.25 
Dry Ash 10.70 
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The coal was pulverized to provide particles sufficiently small to pass 
through a 200 mesh Tyler screen. A mixture of pulverized coal, previously 
extracted hydrogenated coal oil solvent having been hydrogenated to remove 
at least about 80% of the asphaltenes and hydrogen was charged to a 
liquefaction zone maintained at the following conditions: a pressure of 
2500 psig., a temperature of 420.degree. C. (788.degree. F.), a solvent to 
coal ratio of 2:1 by weight, a liquid hourly space velocity (LHSV) of 0.8 
hr..sup.-1 and a hydrogen circulation rate of 10,000 standard cubic feet 
per barrel of coal slurry. The effluent from the liquefaction zone was 
admitted to a gas separator to remove unconsumed hydrogen and any other 
gas present. The liquid coal slurry recovered from the gas separator was 
admixed with toluene solvent to provide a solvent to slurry ratio of 3.5:1 
by weight and with fresh hydrogenated coal oil solvent to provide a coil 
oil solvent to slurry ratio of 1:8. 
The mixture of toluene, fresh coil oil solvent and coal slurry was charged 
to a separation zone comprising a centrifuge which is operated at a 
temperature of 75.degree. C. and a pressure of 100 psig. to remove ash and 
unconverted coal from the valuable liquid hydrocarbons. Said liquid 
hydrocarbons were admitted to a solvent recovery zone which is maintained 
at a temperature sufficient to recover the toluene solvent. The resulting 
ash-free, solvent-free hydrocarbon stream is charged to a hydrogenation 
zone which contains a cobalt-molybdenum-alumina catalyst and which is 
maintained at the following conditions: a pressure of 2000 psig., a 
temperature of 735.degree. F., a liquid hourly space velocity of 1.0 
hr..sup.-1 and a hydrogen circulation rate of 9000 SCFB. The resulting 
hydrogenation hydrocarbon was recovered as product which contained 89.8% 
carbon and 9.3% hydrogen. A portion of the product was recycled to provide 
the hydrogenated coal oil solvent having been hydrogenated to remove at 
least about 80% of the asphaltenes used in the liquefaction zone and in 
the pre-mix zone. The recovered product represented a 70% recovery of the 
coal charged to the liquefaction zone. 
The foregoing specification and illustrative example clearly indicate the 
means by which the present invention is effected, and the benefits 
afforded through the utilization thereof.