Hydrogenation of coal liquid utilizing a metal carbonyl catalyst

Coal liquid having a dissolved transition metal, catalyst as a carbonyl complex such as Co.sub.2 (CO.sub.8) is hydrogenated with hydrogen gas or a hydrogen donor. A dissociating solvent contacts the coal liquid during hydrogenation to form an immiscible liquid mixture at a high carbon monoxide pressure. The dissociating solvent, e.g. ethylene glycol, is of moderate coordinating ability, while sufficiently polar to solvate the transition metal as a complex cation along with a transition metal, carbonyl anion in solution at a decreased carbon monoxide pressure. The carbon monoxide pressure is reduced and the liquids are separated to recover the hydrogenated coal liquid as product. The dissociating solvent with the catalyst in ionized form is recycled to the hydrogenation step at the elevated carbon monoxide pressure for reforming the catalyst complex within fresh coal liquid.

BACKGROUND OF THE INVENTION 
The present invention relates to methods of hydrogenating liquid-coal 
intermediates and products such as those produced in conventional coal 
liquefaction processes and solvent refined coal processes. For purposes of 
this application the term "coal liquid" is intended to include 
carbonaceous liquids derived from anthracite, bituminous, and lignite coal 
as well as similar liquids from peat, oil shale, tar sand, wood, lignin, 
solid petroleum residuals and other related materials. 
The coal liquids produced by well-known coal liquefaction processes include 
a mixture of aromatic compounds including but not limited to benzene, 
naphthalene, anthracene, methylindan, decalin and derivatives of these 
compounds. Tars, bitumens, asphaltenes, other higher boiling compounds and 
ash may also be included. It is desirable to further hydrogenate these 
coal liquids and separate them from solid materials to make them suitable 
for use as fuel oils and feed stock for the production of refined fuels. 
Previous methods for hydrogenating and liquefying coal and coal liquids 
have included the use of heterogeneous catalysts. Solid catalysts 
including compounds of cobalt, iron, nickel, molybdenum or tungsten 
deposited on silico-aluminates or other appropriate supports are contacted 
with the coal liquid in the presence of hydrogen or a suitable hydrogen 
donor in solution. Molten salts such as zinc chloride also are employed as 
catalysts. Such heterogeneous systems must include sufficient reaction 
surfaces available to both the hydrogen and the coal liquid to allow the 
reaction to proceed at an acceptable rate. Much more intimate contact is 
possible with homogeneous systems in which the catalyst is dissolved 
within the liquid undergoing hydrogenation. However, in the homogeneous 
systems, the separation of product and catalyst has been an extremely 
difficult problem. 
PRIOR ART STATEMENT 
The following publications relate to the technical field of the subject 
invention but do not disclose or make obvious the invention as claimed. 
ERDA-77-33, Fossil Energy Research Program of the Energy Research and 
Development Administration FY 1978, pages 33-47. This report briefly 
describes a number of processes for the liquefaction and hydrogenation of 
coal and coal liquids. Many of these processes, such as the H-coal, 
synthoil and zinc chloride process, employ solid or molten salt catalysts 
in contact with coal liquids. Others employ solvents for extracting 
hydrocarbons from the coal, such as the solvent refined coal (SRC), 
solvent extraction of lignite and the CO-STEAM processes. In none of these 
is a homogeneous catalyst employed which is separated from the product in 
the manner described herein. 
Mertzweiller, U.S. Pat. No. 2,841,617, 1 July 1958. This patent describes a 
decobalting method for use with the Oxo process for the production of 
aldehydes from olefins reacted with carbon monoxide and hydrogen. 
Decobalting is achieved by converting cobalt hydrocarbonyl to its 
water-soluble cobalt compound, Co(Co(CO).sub.4).sub.2 by reaction with a 
concentrated aqueous solution of cobaltous ions. 
Neither of these references disclose the novel coal liquid hydrogenation 
process summarized below. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of 
hydrogenating a coal liquid through use of a transition metal catalyst 
dissolved as a complex molecule within the coal liquid. 
It is also an object to provide a coal liquid hydrogenation method in which 
the homogeneous catalyst is conveniently separated and recovered from the 
product liquid. 
It is a further object to provide a coal liquid hydrogenation method in 
which solid mineral matter is separated from the product. 
In accordance with the present invention, coal liquid having a dissolved 
transition metal catalyst as a carbonyl complex is hydrogenated with 
hydrogen gas in the presence of a relatively high partial pressure of 
carbon monoxide. During hydrogenation, the coal liquid is contacted with 
an immiscible, dissociating solvent selected from one of the hydroxylic 
liquids including ethylene glycol, propylene glycol, diethanolamine, 
triethanolamine and mixtures of these liquids. These dissociating solvents 
are of moderate coordinating ability while sufficiently polar to solvate 
the transition metal and form ions when the carbon monoxide partial 
pressure is reduced to a level substantially lower than that occuring 
during hydrogenation. The ionized form of the catalyst is extracted into 
the dissociating solvent which can be separated from the hydrogenated coal 
liquid. The hydrogenated coal liquid is removed as product and the 
dissociating solvent including the dissolved catalyst is recycled into 
immiscible mixture with fresh coal liquid at the higher partial pressure 
of carbon monoxide. The catalyst is reformed into the complex molecule of 
the transition metal carbonyl in solution within the coal liquid to again 
function as a homogeneous hydrogenation catalyst. 
In other more specific aspects of the invention, the dissociating solvent 
is ethylene glycol and ethylene glycol-water mixtures having up to 20% by 
weight water. The catalyst is dicobalt octacarbonyl as a complex molecule 
dissolved in the coal liquid and a solvated cobaltous cation along with 
tetracarbonyl cobaltate anion dissolved within the glycol. Also, the 
inventors have found that this combination of glycol and catalyst 
preferentially sweeps mineral matter including ash and other solid 
particles from the coal liquid into the glycol phase to permit their 
separation from the product.

DETAILED DESCRIPTION OF THE INVENTION 
In the FIGURE a hydrogenator 11 is fed with a coal liquid 13 and a hydrogen 
and carbon monoxide gas mixture 15. In addition, a solvent 17 including a 
recycle stream 19 which contains recovered catalyst is fed into the 
hydrogenator. 
Hydrogenator 11 is basically a reactor in which hydrogen is brought into 
contact with coal liquid including a dissolved catalyst. The catalyst is 
transferred to the coal liquid from the solvent 17 as the two immiscible 
liquids are intimately mixed within the hydrogenator 11. For these 
purposes, hydrogenator 11 can be an agitated vessel for suitably mixing 
the immiscible liquids and the gases in intimate contact. Other unit 
operations and equipment such as packed liquid-gas contacting towers or 
baffled flow-through chambers as well as various other known liquid-liquid 
and liquid-gas contactors can be employed as hydrogenator 11. 
The mixture of hydrogenated coal liquid, solvent and entrained gases are 
passed to a separator 23 maintained at a lower temperature than the 
hydrogenator 11. As an example, the hydrogenator may be operated at about 
200.degree.-230.degree. C. while separator 23 is cooled to about 
100.degree.-130.degree. C. to enhance separation of the various streams. 
Cooling can be achieved by heat exchange communication between the mixture 
21 and other process streams such as recycle 19 as well as outside coolant 
flows. 
Within separator 23, the entrained gases and two different liquid phases 
are separated into their respective flows with the solid mineral matter 
passing into the solvent phase. The gases are withdrawn at 25 to provide a 
substantially reduced partial pressure of carbon monoxide and thereby 
shift the catalyst from the hydrogenated coal liquid to the solvent. The 
vented gases at 25 can be treated by conventional methods to adjust the 
various component concentrations, e.g. those of CO, H.sub.2, H.sub.2 S, 
NH.sub.3 and CO.sub.2. The gas flow can then be compressed to the 
hydrogenator for use with the entering H.sub.2, CO flow at 15. 
The hydrogenated coal liquid is removed as product at 27 and the 
dissociating solvent containing the catalyst and solid mineral matter, 
e.g. ash, is treated and recycled at 19 to the hydrogenator 11. A portion 
of product 27 may also be recycled to the coal liquid feed 13 to reduce 
density and viscosity of the feed. The solvent is withdrawn from separator 
23 at 28 and passed to a solid-liquid separation unit 29, such as a filter 
or centrifuge, for removing solid mineral matter 30. The mineral matter is 
washed at 31 with water and removed from the process at 33. The resulting 
solvent and wash water mixture 35 is combined with the solvent flow and 
fed to a suitable evaporator 37 where the solvent is concentrated by water 
evaporation prior to recycle at 19 to the hydrogenator. 
Since the dissociating solvent and catalyst are recycled to hydrogenator 
11, only small amounts to make up for losses will need to be added after 
the initial charge. The catalyst can be added into either the coal liquid 
or the solvent as the complex molecule or the ionic form. Other forms such 
as an acetate salt of, for instance, cobalt may also be a suitable form 
for providing the catalyst. 
The process equipment employed in implementing the separations portion of 
the present method are well-known conventional unit operation components. 
Separator 23 can be a settling tank or a decanter for permitting gravity 
separation of the immiscible liquids and solids. Other known operations 
such as a liquid centrifuge can also be used. Suitable and well-known 
pressure-regulating devices and compressors are used to ensure that the 
partial pressure of carbon monoxide within separator 23 is substantially 
less than that within reactor 11. 
Washer 31 for removing adherent liquid from mineral matter 33 and 
evaporator 37 are well-known chemical engineering unit operations. For 
instance, the washing can be performed in a suitably drained trough or 
container and the evaporator can be a single-stage unit or a stripping 
column. 
Coal liquid 13 is one that has been prepared through processes such as 
solvent extraction of coal or other carbonaceous solids, or through 
preliminary hydrogenation and liquefaction processes. This liquid includes 
high-boiling and high-molecular-weight cyclic aromatic materials that can 
be substantially upgraded in terms of lower viscosity, lower density, 
lower boiling point and improved burning characteristics through 
hydrogenation. Various aromatic liquids such as benzene, naphthalene, 
anthracene, pyrene, perylene, benzothiophene quinoline and the derivatives 
of these polycyclic compounds may be present. In addition, 
high-molecular-weight coal tars, bitumens, asphaltenes, coal particles and 
ash may be in the coal liquid feed. 
The hydrogen and carbon monoxide gas stream 15 can be obtained conveniently 
from the product of a coal gasification process. Consequently, other gases 
such as methane, nitrogen, oxygen and carbon dioxide may be included. This 
gas flow will ordinarily include about 20 to 50% hydrogen and about 20 to 
60% carbon monoxide by volume. The carbon monoxide will generally be in 
excess or about 1 to 1.6 times that of the hydrogen. 
As will be seen, the carbon monoxide partial pressure is maintained at a 
high level within hydrogenator 11 in comparison to that in separator 23. 
For example, a carbon monoxide partial pressure of 10 to 50 MPa (mega 
pascal) may be present in the hydrogenator, while only 50 to 500 kPa (kilo 
pascal) pressure is employed in separator 23. Preferably a carbon monoxide 
partial pressure of at least 15 MPa is used in the hydrogenator. 
Solvent 17 is a dissociating solvent that is a hydroxylic liquid capable of 
dissociating the catalyst used in the hydrogenation process to ions. The 
solvent is also of moderate coordinating ability such that it competes 
with carbon monoxide for the transition metal. A low carbon monoxide 
pressure causes the complex molecule form of the catalyst to dissociate 
into a transition metal cation and a transition metal, carbonyl anion. 
This ionic form of the catalyst is preferentially extracted into the 
dissociating solvent at the lower carbon monoxide pressure within the 
separator. The preferred dissociating solvent is ethylene glycol or 
mixtures of ethylene glycol and up to 20% by weight water. The combination 
of ethylene glycol and the catalyst draws the suspended particles of 
mineral matter into the glycol phase for subsequent separation. In 
addition to ethylene glycol, various other hydroxylic liquids which are 
immiscible with the coal liquid are expected to be suitable for use. These 
other liquids include propylene glycol, glycerol, diethanolamine and 
triethanolamine. 
The catalyst used is a transition metal, carbonyl catalyst, for instance 
dicobalt octacarbonyl Co.sub.2 (CO).sub.8, molybdenum hexacarbonyl 
Mo(CO).sub.6, dimanganese decacarbonyl Mn.sub.2 (CO).sub.10, iron 
pentacarbonyl Fe(CO).sub.5 and triiron dodecacarbonyl Fe.sub.3 
(CO).sub.12. Of these transition metal carbonyls, Co.sub.2 (CO).sub.8 is 
preferred as it has exhibited good catalytic activity, but it is 
reasonable to assume that some catalytic activity and recoverability would 
be exhibited by these other transition metal, carbonyl catalysts. 
Within the system the catalyst appears in two forms, the complex molecule 
dissolved within the coal liquid, e.g. Co.sub.2 (CO).sub.8, and the 
solvated ionic form, e.g. Co.sup.+2 (solvated with ethylene glycol) and 
Co(CO).sub.4.sup.-. The cobalt carbonyl catalyst transfers between the 
coal liquid as a complex molecule and the dissociating solvent in the 
solvated ionic form in response to the change in carbon monoxide pressure. 
The relatively high carbon monoxide pressure within the hydrogenator 
drives the catalyst into the coal liquid while the reduced carbon monoxide 
pressure within the separator permits the catalyst to dissociate into the 
ionic form which is preferentially soluble within the dissociating 
solvent. The following reaction is typical 
##STR1## 
After reducing the carbon monoxide pressure in separator 23, the 
dissociating solvent with the catalyst settles or is otherwise separated 
from the hydrogenated coal liquid product 27. The solvent and catalyst is 
then recycled to the hydrogenator to again be included in an immiscible 
mixture with fresh coal liquid feed 13. Mineral matter and some of the 
solvent can be withdrawn at 30 and water washed to remove relatively clean 
ash and mineral solids 33 from the process. As described, water can be 
removed from the solvent by an evaporation or distillation operation at 37 
and the solvent returned to the hydrogenator. Alternatively, where the 
solvent is ethylene glycol a fairly high percentage of water can be 
tolerated, e.g. up to 20 weight percent, such that intermittent 
evaporation of the water from the solvent is permissible. 
In accordance with the invention the dissociating solvent is recycled into 
contact with fresh coal liquid for return of the catalyst to the process. 
Suitable adaptations can be made to operate the process either 
continuously as indicated or in batch steps. The feed into and discharge 
from both the hydrogenator and the separator can accordingly either be 
performed intermittently or continuously. 
The following example is presented merely to illustrate operation of the 
present process. 
EXAMPLE 
About 200 volume parts of ethylene glycol containing about 5% water by 
weight is blended with about 1000 volume parts of coal liquid blended with 
product so as to have a density of 1.07 g/cc. The resulting immiscible 
liquid mixture is agitated in the presence of 30 MPa total pressure 
including carbon monoxide and hydrogen in a mole ratio of about 1:1 and a 
temperature of about 220.degree. C. Sufficient Co.sub.2 (CO).sub.8 is 
added into the ethylene glycol phase to obtain about 1.7% by weight Co 
before filling into the hydrogenator. After hydrogenation for about 16 
hours, the immiscible liquid mixture is passed through a separator where 
the carbon monoxide partial pressure is reduced to about 50 kPa at a total 
pressure of about 100 kPa (1 atmosphere). After settling for about 16 
hours, the hydrogenated coal liquid is removed as an upper liquid phase as 
product and the more dense ethylene glycol phase with the catalyst in 
solvated ionic form is recycled to the hydrogenator. Ash and other mineral 
matter are drawn from the bottom of the glycol phase. Table I illustrates 
the upgrading of the coal liquid by the present process. 
TABLE I 
__________________________________________________________________________ 
Density 
Heating 
Mineral 
Viscosity 
g/cc value 
H/C S % 
N % 
O % 
matter 
mPa s 24.degree. C. 
24.degree. C. 
J/kg 
__________________________________________________________________________ 
Coal 
liquid 
1.03 
0.44 
1.08 
2.85 
1.31 44.9 1.07 3 .times. 10.sup.7 
Product 
1.13 
0.35 
0.67 
1.35 
0.35 37.1 1.045 
3.2 .times. 10.sup.7 
__________________________________________________________________________ 
It will be clear from the above that the present invention provides a 
process for the hydrogenation and upgrading of coal liquid through the use 
of a homogeneous catalytic reaction. The catalyst is recoverable in a 
dissociating solvent phase and conveniently returned to the hydrogenation 
step. Ethylene glycol used as a dissociating solvent with the catalyst 
provides the additional advantageous feature of selectively wetting and 
removing finely divided particles of mineral matter from the coal liquid 
product.