Hydroliquefaction of coal

Coal is catalytically hydroliquefied by passing coal dispersed in a liquefaction solvent and hydrogen upwardly through an expanded catalyst bed in a stream having a cross-sectional flow area of no greater than 255 inches square, with the stream through the catalyst bed having a length and a liquid and gas superficial velocity to maintain an expanded catalyst bed and provide a Peclet Number of at least 3. If recycle is employed, the ratio of recycle to total feed (coal and liquefaction solvent) is no greater than 2:1 based on volume. Such conditions provide for improved selectivity to liquid product to thereby reduce hydrogen consumption.

This invention relates to the hydroliquefaction of coal. 
Hydroliquefaction of coal to valuable liquid products is currently of great 
interest. In one such process, coal dispersed in a suitable liquefaction 
solvent is hydroliquefied in an upflow expanded or ebullated 
hydroliquefaction catalyst bed. Such a process is described, for example, 
in U.S. Pat. No. 2,987,465. 
Applicant has found that such an upflow expanded or ebullated bed 
hydroliquefaction process has poor selectivity to liquid products, whereby 
there is an inefficient use of hydrogen and the production of substantial 
amounts of light products, such as methane, ethane, propane, butane and 
light oils boiling below 400.degree. F. Such products contain a higher 
percentage of hydrogen than heavier distillates. 
In accordance with the present invention, applicant has provided a new and 
improved process and system for the hydroliquefaction of coal in an upflow 
expanded or ebullated catalyst bed which increases the selectivity to 
liquid products and thereby efficiently uses its hydrogen to provide a 
more economical process. 
In accordance with one aspect of the present invention, there is provided a 
process for the catalytic hydroliquefaction of coal by passing coal 
dispersed in a coal liquefaction or pasting solvent and hydrogen through 
at least one upflow expanded catalyst bed in a stream having a 
cross-sectional flow area of no greater than 255 square inches, with the 
stream through the catalyst bed having a length and a gas and liquid 
superficial velocity to maintain an expanded bed and provide a Peclet 
Number of at least 3. If recycle is employed, the ratio of recycle to 
total feed (coal and liquefaction solvent) does not exceed 2:1, by volume. 
In accordance with another aspect of the present invention, there is 
provided a reaction system for the catalytic hydroliquefaction of coal 
which includes at least two upflow expanded or ebullated bed catalytic 
reaction zones in series, each of which includes an expanded catalyst bed 
providing for flow therethrough in a stream which has a cross-sectional 
flow area of no greater than 255 square inches and a flow length whereby 
the superficial velocities of gas and liquid through the reaction zones 
maintain the expanded or ebullated catalyst bed and provide a Peclet 
Number of at least 3. 
Peclet Number is defined as follows: 
##EQU1## 
wherein 
V.sub.L is liquid velocity, ft/hr. 
L is length of reactor, ft. 
D is the equivalent diameter of the catalyst reaction zone 
V.sub.G is the gas velocity, ft/hr 
E.sub.G is the fraction of the total catalyst bed volume which is occupied 
by the gas, as disclosed by Hughmark, G. A., "Hold-Up and Mass Transfer in 
Bubble Columns" I&EC Process Design and Development, 6" (2), pp 218-220, 
1964. 
Peclet Number is a measure of the approach to plug flow, with a Peclet 
Number of infinity corresponding to perfect plug flow. In accordance with 
the present invention, the higher the Peclet Number the better the 
hydrogen efficiency, and as a result, although a Peclet Number of at least 
3 provides a beneficial increase in hydrogen efficiency, the Peclet Number 
should preferably be as high as possible, consistent with other reaction 
conditions. Thus, the Peclet Number is preferably at least 3, and most 
preferably at least 10. The Peclet number is preferably as high as 
possible; however, as a result of design limitations the Peclet number 
generally does not exceed 70, and in most cases does not exceed 50. The 
selection of an optimum Peclet Number for a particular feedstock and other 
designs considerations should be apparent to those skilled in the art from 
the teachings herein. 
The cross-sectional flow area of the stream in the catalyst bed is no 
greater than 255 square inches, with the cross-sectional flow area 
generally being at least 10 square inches. In most cases, the 
cross-sectional flow area is at least 28 square inches. The selection of 
an optimum cross-sectional flow area will vary, and the selection of such 
an optimum cross-sectional flow area is deemed to be within the scope of 
those skilled in the art from the teachings herein. 
The other parameters included in the calculation of Peclet Number are 
reaction zone length and superficial gas and liquid velocities through the 
expanded catalyst bed. The velocity of gas and liquid through the bed must 
be at a value sufficient to maintain the ebullated or expanded catalyst 
bed state, and as a practical manner, such expansion is primarily related 
to the superficial liquid velocity. Thus, the reactor length and the 
superficial liquid and gas velocities are coordinated to provide a Peclet 
Number, as hereinabove described, as well as sufficient velocity to 
provide for the expanded or ebullated catalyst bed. In general the 
reaction zone length is in the order of from 20 to 130 feet, and most 
preferably in the order of from 40 to 90 feet, with the superficial liquid 
velocity generally being in the order of from 0.04 to 0.3 foot per second. 
The superficial gas velocity is generally in the order of from 0.04 to 1 
foot per second. The selection of optimum values is deemed to be within 
the scope of those skilled in the art from the teachings herein. 
In accordance with the invention, recycle is limited, with the ratio of 
recycle to total feed (coal and liquefaction solvent) being no greater 
than 2:1. Although in some cases it may be possible to operate the process 
without any recycle; i.e., a recycle ratio of 0:1, in most cases, some 
recycle is required in order to maintain a sufficient liquid velocity for 
expanding the catalyst bed. As a result, in most cases, the recycle ratio 
is at least 0.2:1, with the recycle ratio generally not exceeding 1:1. In 
accordance with the preferred embodiment, all of such recycle is provided 
externally; i.e., no internal recycle, which thereby eliminates the 
necessity for an internal recycle pump as generally employed in the 
ebullated bed coal liquefaction process. It is to be understood, however, 
that it is possible within the scope of the invention to provide some 
internal recycle, provided that the recycle ratio (internal and/or 
external recycle) does not exceed 2:1. 
In accordance with a preferred embodiment of the present invention, there 
are at least two catalytic hydroliquefaction zones of the type hereinabove 
described in series, and preferably at least three such zones in series. 
The additional hydroliquefaction zones are employed to provide the desired 
hydroliquefaction without an unacceptable increase in temperature; i.e., 
the exothermic heat of reaction is controlled by providing a series of 
reaction zones, rather than by providing large quantities of recycle. The 
selection of an optimum amount of reaction zones, in series, is deemed to 
be within the scope of those skilled in the art from the teachings herein. 
In most cases, it is not necessary to provide any more than 4 of such 
hydroliquefaction zones in series. In most cases, the number of 
hydroliquefaction zones in series is selected to limit the temperature 
increase of each of the zones to no greater than 150.degree. F., and 
preferably to no greater than 100.degree. F. 
The hydroliquefaction, as known in the art, is conducted at elevated 
temperatures and pressures. In general, the hydroliquefaction temperature 
is in the order of 650.degree. F. to 900.degree. F., and preferably from 
750.degree. F. to 850.degree. F. The pressures are generally in the order 
of from 1800 to 3000 psig, and most generally in the order of from 2000 to 
2700 psig. The selection of optimum temperatures and pressures are deemed 
to be within the scope of those skilled in the art from the teachings 
herein. 
Hydrogen is introduced into the hydroliquefaction zone in an amount, which 
when coordinated with the other processing conditions, provides an amount 
of hydrogen addition or absorption to provide the desired liquefied 
product. In addition, hydrogen is provided for effecting 
hydrodesulfurization and hydrodenitrification of the feedstock. In 
general, by proceeding in accordance with the present invention, it is 
possible to achieve a conversion of 90% or more of the MAF coal feed with 
hydrogen consumptions in the order of from 2 to 4 lbs. of hydrogen per 100 
lbs. of coal. 
The hydroliquefaction is conducted with a catalyst suitable for liquefying 
the coal, and in addition, such catalyst should have desulfurization and 
denitrification activity. Such catalysts are generally known in the art; 
e.g., cobalt molybdate, nickel molybdate, tungsten-nickel sulfide, etc., 
and are generally supported on a suitable support such as alumina. The 
selection of a suitable catalyst is deemed to be within the scope of those 
skilled in the art from the teachings herein. 
The catalyst is maintained in the hydroliquefaction zone as an expanded or 
ebullated bed. As known in the art, such expanded or ebullated bed differs 
from a fluidized bed in that, in the expanded or ebullated bed, catalyst 
particles are not maintained in fluidized random motion. Such expanded or 
ebullated beds are known in the art, and as a result, no further details 
in this respect are deemed necessary for a complete understanding of the 
present invention. 
The coal, as known in the art, is dispersed in a suitable pasting or coal 
liquefaction solvent or oil for passage through the catalytic 
hydroliquefaction zone. Such pasting or liquefaction solvents are known in 
the art, and is preferably a solvent derived from the coal liquefaction 
product, although other pasting solvents or oils may also be employed for 
the hydroliquefaction. The selection of a particular pasting oil is well 
within the scope of those skilled in the art, and forms no part of the 
present invention. In general, as known in the art, the pasting solvent is 
provided in an amount to provide a pasting solvent to coal weight ratio in 
the order of those generally used in the art; e.g., from 1:1 to 20:1. 
The coal employed as a hydroliquefaction feed may be a bituminous coal, 
sub-bituminous coal or a lignitic coal. The selection of a suitable coal 
for producing a desired product forms no part of the present invention, 
and as a result no further details in this respect are deemed necessary 
for a complete understanding thereof.

It is to be understood that the embodiment is only schematically shown, and 
various equipment, such as pumps, heat exchangers and the like have been 
omitted for simplifying the description of the embodiment. The use of such 
equipment at suitable places is well within the scope of those skilled in 
the art from the teachings herein. 
Referring now to the drawing, coal in line 10 and a suitable pasting 
solvent in line 11, generally recovered from the hydroliquefaction 
product, are introduced into a slurry tank 12 to disperse the coal in the 
pasting solvent. A slurry of coal in pasting solvent is withdrawn from 
tank 12 through line 13, combined with recycle in line 14, as hereinafter 
described, and the combined stream in line 15 is introduced into the first 
of three hydroliquefaction reactors 16, 17 and 18, respectively. Heated 
hydrogen in line 19 is also introduced into the first of the three 
hydroliquefaction reactors 16, 17 and 18. 
Each of the hydroliquefaction reactors 16, 17 and 18 includes an expanded 
or ebullated bed of hydroliquefaction catalyst, and such reactors are 
designed and operated to provide for upward flow of hydrogen and coal 
dispersed in solvent through the bed as a stream having a cross-sectional 
flow area through the catalyst of no greater than 255 square inches, and a 
Peclet Number of at least 3. Reactors 16, 17 and 18 are operated without 
any internal recycle. Thus, as hereinabove described, the length of each 
of the catalyst beds as well as the liquid and gas superficial velocities 
are coordinated with the stream cross-sectional flow area through the 
catalyst to provide a Peclet Number of at least 3. The hydroliquefaction 
reactors 16, 17 and 18 are operated at the temperatures and pressures 
hereinabove described to effect hydroliquefaction of the coal, and in 
addition, hydrodesulfurization and hydrodenitrification thereof. The coal 
dispersed in the pasting solvent, as well as the hydrogen, flows serially 
through the expanded hydroliquefaction catalyst beds in reactors 16, 17 
and 18, with the hydroliquefaction effluent being withdrawn from reactor 
18 through line 21. 
The effluent in line 21 is introduced into a gas-liquid separator 22 to 
recover a portion of the liquid product in line 23, with the remaining 
portion of the effluent in line 24 being passed through a suitable cooler 
25 and introduced into a second separator 26 to recover further liquid 
product through line 27. The net hydroliquefaction product is recovered 
through line 28 for further treatment, as known in the art. 
Recycle product is recovered through line 14, and as hereinabove note, the 
recycle in line 14 is primarily for the purpose of providing sufficient 
liquid in the hydroliquefaction reactors 16, 17 and 18 to maintain the 
catalyst as an expanded bed. The recycle amounts are limited as 
hereinabove described. 
Gas is recovered from separator 26 through line 31 and a portion thereof is 
purged through line 32. The remaining portion is compressed in compressor 
33, combined with make-up hydrogen in line 34 and the combined stream 
passed through a suitable heater 35 to provide heated hydrogen to the 
hydroliquefaction through line 19. 
The hereinabove described embodiment is only illustrative of the present 
invention, and as a result, such an embodiment may be modified within the 
spirit and the scope of the present invention. Thus, the hydroliquefaction 
may be effected in more or less than three zones, as particularly 
described. Similarly, product recovery may be effected other than as 
particularly described. 
These and other modifications should be apparent to those skilled in the 
art from the teachings herein. 
The invention will be further described with respect to the following 
Example; however, the scope of the invention is not to be limited thereby: 
EXAMPLE 
The hydroliquefaction is conducted by the use of two reactors in series, 
each of which has a nominal diameter of 1 inch and a length of 10 feet. 
Each of the reactors includes a catalyst of cobalt molybdate supported on 
alumina. 
The hydroliquefaction conditions are used for the hydroliquefaction of 
Illinois No. 6 Coal. 
Feed Coal Content, wt. % 33.5 
Reaction Temperature, .degree.F. 780-820 
Reaction Pressure, psig. 1400 
Liquid Feed velocity, ft/hr 116 
Gas Feed velocity, ft/hr 1513 
Peclet Number 20 
Reaction Stages per Reactor 10 
Hydrogen consumption, wt. % of (1) coal feed 3.7 
Sulfur content of ash free liquefaction product, wt. % 0.45 
FNT (1) The coal liquefaction solvent was not equilibrated and some of the 
hydrogen consumption is attributable to reaction with liquefaction 
solvent. 
The present invention is particularly advantageous in that there is 
provided improved selectivity to liquid product which increases overall 
hydrogen efficiency. As a result, the present process is more economic 
than the hydroliquefaction processes previously employed in the art. 
Thus, by proceeding in accordance with the invention it is possible to 
achieve a 90% or greater conversion of moisture ash free (MAF) coal with 
hydrogen consumptions of 2-4 lbs. hydrogen per 100 lbs. coal, as compared 
to previous hydrogen consumptions in excess of 4%, and in most cases in 
excess of 4.5%. 
These and other advantages should be apparent to those skilled in the art 
from the teachings herein. 
Numerous modifications and variations of the present invention are possible 
in light of the above teachings and, therefore, within the scope of the 
appended claims, the invention may be practised otherwise than as 
particularly described.