Zinc sulfide liquefaction catalyst

A process for the liquefaction of carbonaceous material, such as coal, is set forth wherein coal is liquefied in a catalytic solvent refining reaction wherein an activated zinc sulfide catalyst is utilized which is activated by hydrogenation in a coal derived process solvent in the absence of coal.

BACKGROUND OF THE PRIOR ART 
The liquefaction of solid carbonaceous material, such as coal, in the 
presence of a solvent has been practiced since the early years of the 
twentieth century. Such liquefaction or solvent refining process has been 
performed predominently on a non-commercial basis due to the expense of 
performing the process to derive utilizable liquid and solid fuels and 
because of the relatively less expensive availability of liquid fuels from 
petroleum. Large scale production of liquefied fuels from coal was 
performed in Germany when petroleum was unavailable to that country during 
the war years. 
With the increasing expense and scarcity of petroleum and the liquid fuels 
derived therefrom, increased interest in the liquefaction or solvent 
refining of solid carbonaceous materials, such as coal, to liquid and 
solid refined products has occurred. However, the technical difficulties 
in achieving high yields of liquid products from coal at relatively 
economical rates has still presented a problem for those in the art. The 
most popular solution to the production of high yields of the desired 
liquid products from solid carbonaceous material, such as coal, has been 
the use of metal catalysts such as molybdenum, cobalt, nickel, tungstun 
oxides and sulfides. Such catalysts improve the proportion of liquid 
product as well as the overall conversion of coal to solid refined 
products, known as solvent refined coal (SRC) and oils. However, these 
metal catalysts are expensive and constitute an undesirable increase in 
the cost of liquid fuel production from solid carbonaceous material or 
coal. This is particularly true of coal conversion reactions wherein 
increased carbon fouling and metal and sulfide contamination of catalysts 
over that expected in petroleum refining occurs, with the resulting effect 
of diminishing the effective life of the catalyst in the reaction zone. 
This requires either the regeneration of the fouled metal catalysts or the 
disposal of the catalyst and the replacement of the same with additional 
fresh catalyst. When such expensive metal catalysts are utilized, both of 
these modes of operating the catalyzed reaction of coal are deemed to be 
undesirable from an economic point of view when operating the coal 
liquefaction process in a commercial manner wherein the resulting liquid 
product must be competitive with the remaining petroleum products still 
presently available. One alternate solution to this problem has been to 
utilize inexpensive coal liquefaction catalysts which can be thrown away 
after their effective catalytic life has expired without adversely 
affecting the economic operation of a commercially run coal liquefaction 
process. The difficulty in this solution is that many relatively 
inexpensive catalysts do no have significant or desirable levels of 
catalytic activity for the liquefaction of coal or other solid 
carbonaceous material. Because of this drawback, yet another attempt at a 
solution to the creation of an economic and efficient liquefaction process 
has been the combination of relatively inexpensive catalysts with small 
amounts of expensive catalysts. 
For example, in U.S. Pat. No. 1,946,341, the hydrogenation of petroleum and 
coal tars in the presence of hydrogen sulfide and a metal sulfide 
catalyst, such as iron, cobalt or nickel sulfide is set forth. 
Alternately, in U.S. Pat. No. 2,227,672, a process for the thermal 
treatment of carbonaceous materials, such as oil or coal is set forth 
wherein a co-catalyst system is utilized. Preferably, a large proportion 
of inexpensive catalyst of low activity is combined with a small 
proportion of a relatively expensive catalyst of high activity. The 
inexpensive catalysts include various metal sulfides such as ferrous, 
manganous and zinc sulfides. The expensive catalyst are generally chosen 
from the disulfides of tungsten, molybdenum, cobalt and nickel. Such 
catalysts can be supported on a carrier and activated by various acid 
treatments or gas treatments such as hydrogen contact. Such catalysts can 
be utilized for the destructive hydrogenation of coal as recited in the 
text of the patent. 
In U.S. Pat. No. 2,402,694, the use of iron sulfide catalysts is recited 
for the production of thiols, wherein the iron sulfide catalyst is first 
made more active by gas phase hydrogenation at high temperatures. 
In U.S. Pat. No. 3,502,564, a metal sulfide catalyst, such as nickel, tin, 
molybdenum, cobalt, iron or vanadium, is taught as a catalyst for coal 
liquefaction. The sulfide catalyst is formed in-situ on the coal by the 
reaction of a metal salt with hydrogen sulfide. 
Additionally, U.S. Pat. No. 4,013,545 teaches the hydrogenation and 
sulfiding of an oxidized metal of Group VIII in order to form a 
hydrocracker catalyst for oils. 
Despite these efforts, the prior art has failed to provide an inexpensive, 
throw-away or once-through catalyst which has increased activity for the 
production of liquid products from the liquefaction or solvent refining of 
solid carbonaceous material, such as coal. 
BRIEF SUMMARY OF THE INVENTION 
The present invention comprises a process for the liquefaction or solvent 
refining of solid carbonaceous material, such as coal, at elevated 
temperature and pressure in the presence of a solvent for the carbonaceous 
material or coal, hydrogen and a hydrogenation catalyst in order to 
produce predominently liquid products or oils and a solid refined product, 
generally known as solvent refined coal (SRC), wherein the improvement 
comprises conducting the liquefaction or solvent refining reaction in the 
presence of an activated zinc sulfide hydrogenation catalyst in which the 
zinc sulfide catalyst is activated prior to utilization by subjecting it 
to hydrogen gas, elevated temperature and a process solvent in the absence 
of the carbonaceous or coal feed material. The activation stage is 
performed under conditions approximating the coal liquefaction or solvent 
refining conditions, but absent the carbonaceous or coal feed material. 
An advantage of the present invention is the utilization of a zinc sulfide 
catalyst which consists of the mineral sphalerite. 
Preferably, the activation stage is performed in the presence of additional 
sulfides in order to avoid the reduction of the zinc sulfide during the 
activation sequence. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention, in which a pretreated, activated zinc sulfide 
catalyst is utilized in a liquefaction or solvent refining process, is 
relevant to the production of liquid fuels from any number of solid 
carbonaceous materials. Such materials include bituminous coal, lignite, 
peat and other organic matter. Preferably, this unique catalyst is 
utilized in the liquefaction or solvent refining of coal to provide liquid 
fuels or oils and solid refined coal material, which is referred to as 
solvent refined coal (SRC). This activated catalyst can be utilized in 
various catalyzed coal liquefaction processes, such as a slurry phase 
liquefaction process, an ebullated bed liquefaction process or a batch 
liquefaction process. 
The process of the present invention, in which an activated zinc sulfide 
catalyst is utilized in a coal liquefaction process, is susceptible of 
operation at a wide variation in the coal liquefaction process parameters. 
For instance, the temperature of the liquefaction reaction may be from 
650.degree. to 900.degree. F. The pressure of the liquefaction reaction 
can be maintained from 500 to 4000 psig. The solvent to coal ratio may 
vary from 80/20 wt % to 60/40 wt %. Finally, the activated zinc sulfide 
catalyst may be utilized in the coal liquefaction reaction in a range of 
0.1 wt % to 10.0 wt %. 
The zinc sulfide utilized in the process of the present invention can be 
pure zinc sulfide of a reagent quality or it may be a beneficiated ore, 
which is sometimes referred to as a concentrate. This form of the zinc 
sulfide is normally in the sphalerite form in which a certain minor 
proportion of the zinc atoms of the zinc sulfide molecule are replaced 
with iron. Sphalerite provides a readily available source of zinc sulfide 
at low cost such that the catalyst may be disposed of after it has become 
deactivated in duty in the coal liquefaction process. 
The activation stage of the zinc sulfide is performed under conditions 
which approximate the coal liquefaction conditions, but in the absence of 
a coal or carbonaceous material feedstock. The zinc sulfide is generally 
provided in a particulate form which can range in size from 100 to 400 
mesh. Alternately, the zinc sulfide catalyst could be supported on an 
inert carrier. The catalyst is placed in process solvent in a proportion 
of 1 wt % to 50 wt % catalyst. The process solvent may be any solvent 
known to be compatible with a coal liquefaction reaction scheme, such as 
creosote oil, internally generated coal derived solvent, solvent taken 
from a hydrotreating process, petroleum derived solvent or a hydrogen 
donor solvent such as tetralin or naphthalene. The appropriate solvent 
should have a boiling point of approximately 420.degree. F. or greater. 
Preferably, the solvent will be the same solvent as is utilized in the 
coal liquefaction process itself. However, the solvent utilized in the 
preactivation of the zinc sulfide catalyst does not have to be the same 
solvent which is utilized in the coal liquefaction reaction. 
The activation of the zinc sulfide is dependent upon the development of a 
hydrogenation atmosphere while the catalyst is at elevated temperature in 
the presence of the process solvent. Therefore, a hydrogen pressure in the 
range of 50 to 5000 psig is necessary in order for this increased activity 
to be produced in the treated catalyst. In addition, it is preferred to 
have at least some additional organic sulfur compounds present in the 
process solvent during activation in order to guard against the reduction 
of the zinc catalyst during the hydrogenation thereof. Activation is 
dependent upon the hydrogen pressure and the temperature during 
activation, but additionally the activation should be performed with a 
residence time in the range of from 5 to 60 minutes. The temperature 
should be in the range of 500.degree. to 900.degree. F. 
When the zinc sulfide has been activated, the activated catalyst and 
process solvent may be directly added to the coal feed material and 
additional process solvent added until the desired feed slurry is present 
for coal liquefaction, or the activated catalyst may be separated from the 
solvent used during activation and the separated catalyst added 
independently into a process solvent and coal feed slurry which is the 
influent for a coal liquefaction process. 
Although the results of this unique activation of zinc sulfide for a coal 
liquefaction process are readily recognizable from the experiments which 
follow, the exact theory as to why the catalyst achieves such increased 
activity after treatment in the presence of hydrogen in process solvent 
are unknown. However, the inventor has observed that the surface area of 
the catalyst is increased dramatically after the activation. Specifically, 
during measurements of the surface area, the zinc sulfide prior to 
activation was ascertained to have a surface area of 1.1 m.sup.2 /g, 
whereas the activated zinc sulfide had a surface area of 4.9 m.sup.2 /g. 
The increase in surface area would appear to account for at least some 
aspect of the increased activity of this catalyst for this particular 
reaction. However, it is believed that additional rearrangement of the 
structure of the zinc sulfide concentrate occurs as shown by x-ray 
diffraction analysis during the pretreatment and activation step, which 
results in a very active zinc sulfide catalyst for coal liquefaction. The 
zinc sulfide concentrate used in the examples in its untreated state was 
identified as having an essentially sphalerite structure. After treatment, 
the x-ray analysis showed that the major phase remained sphalerite, but a 
minor phase existed having a pyrrhotite and triolite structure. 
The following specific examples demonstrate the unexpected activity of zinc 
sulfide and more particularly sphalerite when it is treated with hydrogen 
in the presence of process solvent. The examples show dramatic results 
when compared to unactivated zinc sulfide, particularly with respect to 
the desired production of liquid product, namely oils, from the coal 
feedstock. Although these examples are performed with a particular coal 
starting material, it is contemplated that the liquefaction process 
utilizing the activated catalyst of the present invention is relevant to 
other carbonaceous materials which are susceptible to liquefaction 
reactions. 
The following specific examples show the advantage of using the activated 
catalyst of the present invention. The coal conversion and more 
importantly the oil production resulting from the addition of activated 
zinc sulfide concentrate to a coal liquefaction reaction is shown. The 
comparative data with the uncatalyzed reaction and zinc sulfide which has 
not been activated, regardless of temperature, concentration or specific 
coal is also shown and indicates that the activated zinc sulfide provides 
unexpected improvement in the catalytic activity of this catalyst species 
in a coal liquefaction reaction.

EXAMPLE 1 
This example illustrates the activation procedure of the catalyst. The 
reaction mixture was comprised of zinc sulfide concentrate having a 
composition shown in Table 1 and a process solvent having the elemental 
composition and boiling point distribution shown in Tables 2 and 3, 
respectively. A reaction mixture (10 wt % zinc sulfide concentrate+90 wt % 
solvent) was passed into a one-litre continuous stirred tank reactor at a 
total pressure of 2000 psig and a hydrogen flow rate of 1.33 wt % of 
solvent. The reaction temperature was 850.degree. F. and the nominal 
residence time was 40 minutes. The reaction product was filtered to 
recover the activated zinc sulfide catalyst. The x-ray diffraction 
analysis of the activated catalyst indicated that the sphalerite structure 
of the catalyst was affected by the activation wherein some minor phase 
changes occurred as stated above, and the surface area of the catalyst was 
increased substantially. 
TABLE 1 
______________________________________ 
Weight % 
______________________________________ 
Chemical Analysis of Zinc Sulfide 
Zn 62.6 
S 31.2 
Pb 0.54 
Cu 0.21 
Fe 1.0 
CaO 0.28 
MgO 0.14 
SiO.sub.2 
2.45 
Al.sub.2 O.sub.3 
0.03 
X-Ray Diffraction Analysis 
ZnS, FeS 
(sphalerite type structure) 
______________________________________ 
TABLE 2 
______________________________________ 
Analysis of the Process System 
Weight % 
______________________________________ 
Fraction 
Oil 93.8 
Asphaltene 5.0 
Preasphaltene 0.4 
Residue 0.8 
Element 
Carbon 89.44 
Hydrogen 7.21 
Oxygen 1.70 
Nitrogen 1.10 
Sulfur 0.55 
______________________________________ 
TABLE 3 
______________________________________ 
GC Simulated Distillation of Process Solvent 
Weight % Off Temperature .degree.F. 
______________________________________ 
I.B.P. 519 
5 548 
6 552 
10 569 
20 590 
30 607 
40 627 
50 648 
60 673 
70 699 
80 732 
90 788 
95 835 
97 845 
99 898 
F.B.P. 911 
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EXAMPLE 2 
In this example, the reaction of coal without catalyst is shown. A 3g 
sample of Kentucky Elkhorn #3 coal having the composition shown in Table 4 
was charged to a tubing-bomb reactor having a volume of 46.3 ml. A 6 g 
quantity of solvent, having similar elemental and boiling distributions as 
used in Example 1 was then added to the reactor. The reactor was sealed, 
pressurized with hydrogen to 1250 psig at room temperature and heated at 
850.degree. F. for 60 minutes. It was then agitated at 860 strokes per 
minute for the entire reaction period. After cooling the reaction product 
was analyzed to give a product distribution as shown in Table 5. The 
conversion was 77% based on maf coal, and the oil yield was 16% of feed 
maf coal. 
EXAMPLE 3 
This example illustrates the catalytic effect of unactivated zinc sulfide 
concentrate. To the reactor described in Example 2 was added 3 g of the 
coal used in Example 2 and 6 g sample of the solvent also used in Example 
2. In addition, a 1 g sample of unactivated zinc sulfide concentrate 
described in Table 1 was also added. The reaction and product analysis was 
carried out in the same way as described in Example 2. Conversion was 84% 
of the feed maf coal and the corresponding oil yield was 27% maf coal as 
shown in Table 5, which exceeded the conversion and oil yields of Example 
2 by a significant margin. 
EXAMPLE 4 
In this sample the activated zinc sulfide concentrate was utilized in a 
coal liquefaction reaction. To the reactor described in Example 2 was 
added 3 g of coal and 6 g of solvent of Example 2. In addition, 1 g of 
activated zinc sulfide described in Example 1 was added to the reactor. 
The reaction and product analysis were identical to the method used in 
Example 2. Results are shown in Table 5. The conversion of maf coal was 
96% and the yield of oil was 41% maf. Both values were significantly 
higher than for the no-catalyst reaction in Example 2 and for the 
unactivated zinc sulfide concentrate reaction in Example 3. 
TABLE 4 
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Analysis of Elkhorn #3 Coal 
Weight % 
______________________________________ 
Proximate Analysis 
Moisture 1.81 .+-. 0.03 
Volatile 37.56 .+-. 0.10 
Fixed Carbon 46.03 
Dry Ash 14.60 .+-. 0.02 
Ultimate Analysis 
C 69.40 
H 4.88 
N 1.00 
S 1.94 
O (by difference) 
8.18 
Distribution of Sulfur 
Total Sulfur 1.94 
Sulfate Sulfur 0.04 
Pyrite Sulfur 1.19 
Organic Sulfur 0.75 
______________________________________ 
EXAMPLE 5 
This example illustrates the reaction of coal without any additives. The 
feed slurry was comprised of Kentucky Elkhorn #3 coal having the 
composition shown in Table 4 and a process solvent having the elemental 
composition and boiling point distribution shown in Tables 2 and 3, 
respectively. A coal oil slurry (70 wt % solvent+30 wt % coal) was passed 
into a one-litre continuous stirred tank reactor at a total pressure of 
2000 psig and a hydrogen flow rate of 20,000 SCF/T of coal. The reaction 
temperature was 850.degree. F. and the nominal residence time was 38 min. 
The reaction product distribution obtained was as shown in Table 5. The 
conversion of coal was 81.9% and the oil yield was 20.4% based on maf 
coal. The sulfur content of the SRC was 0.5% and the hydrogen consumption 
was 0.91 wt % of maf coal. 
EXAMPLE 6 
This example illustrates the catalytic effect of unactivated zinc sulfide 
concentrate in a coal liquefaction reaction. The coal and solvent feed 
slurry described in Example 5 was processed in the same reactor described 
in Example 5. Two different temperatures 825 and 850.degree. F. were used 
in Runs 6A and 6B, respectively. zinc sulfide concentrate, without 
activation, having the composition shown in Table 1 was added at a high 
concentration level of 10.0 wt % of slurry. The product distribution 
obtained are shown in Table 10. Conversion of coal and oil yield were 
higher both at 825 and 850.degree. F. temperatures in the presence of 
unactivated zinc sulfide than shown in Example 5, but lower than Example 
4. Hydrogen consumption was significantly higher with unactivated zinc 
sulfide than without it (see Example 5). 
EXAMPLE 7 
This example illustrates the reaction of coal from a different source 
without any additives. The slurry was comprised of Kentucky Elkhorn #2 
coal having the composition shown in Table 6 and a process solvent having 
the elemental composition and boiling point distribution shown in Tables 2 
and 3, respectively. A coal oil slurry (70 wt % solvent+30 wt % coal) was 
passed into a one-litre continuous stirred tank reactor at a total 
pressure of 2000 psig and a hydrogen flow rate of 18,900 SCF/T of coal. 
The reaction temperature was 825.degree. F. and the nominal residence time 
was 35 min. The reaction product distribution obtained was as shown in 
Table 5. The conversion of coal was 85.3% and the oil yield was 12.2% 
based on moisture-ash-free (maf) coal. The sulfur content of the residual 
hydrocarbon fraction (SRC) was 0.61 percent and the hydrogen consumption 
was 0.64 wt % of maf coal. 
EXAMPLE 8 
This example illustrates the catalytic effect of unactivated zinc sulfide 
concentrate at a very low concentration level. The coal and solvent feed 
slurry described in Example 7 was processed at the same reaction 
conditions described in Example 7. Unactivated zinc sulfide concentrate 
was added at a very low concentration level of 1.0 wt % of slurry. The 
product distribution obtained are shown in Table 5. Conversion of coal was 
similar to that shown in Example 7, but oil yield was considerably higher 
than shown in Example 7. Hydrogen consumption was significantly lower than 
shown in Example 7. 
TABLE 5 
__________________________________________________________________________ 
CONVERSION AND PRODUCT DISTRIBUTION ON MAF COAL 
ELKHORN #3 COAL ELKHORN #2 COAL 
EXAMPLE NO. #2 #3 #4 #5 #6A #6B #7 #8 
__________________________________________________________________________ 
Feed Composition 
67/33/0 
60/30/10 
60/30/10 
70/30/10 
60/30/10 
60/30/10 
70/30/0 
69/30/1 
Solvent/Coal/Catalyst (%) 
Catalyst - None = N, Un- 
N U A N U U N U 
activated = U, Activated = A 
Temp., .degree.F. 
850 850 850 850 825 850 825 825 
Time, Min. 60 60 60 38 41 39 35 37.3 
Pressure, psig 1,250* 
1,250* 
1,250* 
2,000.sup.t 
2,000.sup.t 
2,000.sup.t 
2,000.sup.t 
2,000.sup.t 
H.sub.2 Flow, Rate, SCF/T 
-- -- -- 20,000 
26,4000 
24,000 
18,900 
23,500 
Product Distribution, 
wt % MAF Coal 
HC -- -- -- 6.8 5.8 8.9 5.2 4.3 
CO, CO.sub.2 -- -- -- 1.0 1.4 1.5 0.7 1.0 
H.sub.2 S -- -- -- 0.2 0.2 0.2 0.3 0.2 
Oil 16 27 41 20.4 27.3 29.3 12.2 23.0 
Asphaltene 48 43 30 29.2 24.1 22.3 21.2 18.5 
Preasphaltene 13 14 25 25.4 27.3 27.5 44.2 36.8 
I.O.M. 23 16 4 15.8 11.2 7.6 14.7 14.7 
Water -- -- -- 1.2 2.7 2.7 1.5 1.5 
Conversion 77 84 96 81.9 88.8 92.4 85.3 85.3 
Hydrogen Consumption 
-- -- -- 0.91 1.43 1.93 0.64 0.27 
wt % MAF Coal 
SRC Sulfur -- -- -- 0.50 0.65 0.55 0.61 0.76 
Reactor (TB) (CSTR) 
TB TB TB CSTR CSTR CSTR CSTR CSTR 
__________________________________________________________________________ 
*at 77.degree. F., t at reaction conditions 
TB = tubing bomb 
CSTR = continuously stirred tank reactor 
TABLE 6 
______________________________________ 
Analysis of Elkhorn #2 Coal 
Weight % 
______________________________________ 
Proximate Analysis 
Moisture 1.55 
Dry Ash 6.29 
Ultimate Analysis 
C 77.84 
H 5.24 
O 7.20 
N 1.75 
S 1.08 
Distribution of Sulfur 
Total Sulfur 1.08 
Sulfate Sulfur 0.04 
Pyritic Sulfur 0.25 
Organic Sulfur 0.79 
______________________________________ 
As can be seen in a comparison of the varions runs of the examples listed 
in Table 5, oil production is extremely high in Example No. 4 in which 
activated zinc sulfide is utilized as a catalyst to produce liquid oils 
from a solid coal feed material. In addition, the overall conversion is 
significantly higher than all other runs, either in uncatalyzed examples 
or examples using a zinc sulfide catalyst which has not been activated. 
The present invention has been described with reference to a tubing bomb or 
small continuous tank reactor. However, it is understood that the 
invention could be practiced on a commercial level in a continuous mode 
wherein coal slurry is continuously passed into a reaction zone and 
deactivated catalyst and coal products are removed continuously from said 
zone. In such a large scale process, the feed slurry comprising process 
solvent, particulate coal and activated zinc sulfide catalyst in the 
presence of hydrogen is fed through a preheater stage which adjusts the 
temperature to process conditions and then the material is fed into a 
reactor commonly referred to as a dissolver. The main liquefaction or 
solvent refining reactions of the coal feedstock as it is transformed into 
oil and solid solvent refined coal (SRC) occurs in the dissolver. The 
processed and refined slurry, as a product, passes from the dissolver into 
a flash separator where an overhead distillate stream is removed. The 
resulting slurry can be separated into distillate boiling less than about 
850.degree. F. and a residual material containing the ash plus undissolved 
particulate minerals, spent catalyst and amorphous forms of carbon. The 
solids can be separated from the bulk of the product by either filtration 
or by solvent extraction techniques such as critical solvent deashing. 
Although the present invention has been exemplified by the utilization of a 
specific zinc sulfide concentrate and a particular process solvent and 
feed coal, it is understood that the scope of the invention should not be 
limited to the specific examples but rather should be ascertained by the 
claims which follow.