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8/7/2019 catalisis heterogenea licuefaccion dle carbon
1/13
A new process for catalytic liquefaction of coal using dispersed MoS2catalyst generated in situ with added H2O
C. Songa,b,1,*, A.K. Sainia, Y. Yoneyamaa,2
aApplied Catalysis in Energy Laboratory, The Energy Institute, Pennsylvania State University, 209 Academic Projects Building, University Park,
PA 16802, USAbDepartment of Energy and Geo-Environmental Engineering, Pennsylvania State University, 206 Hosler Building, University Park, PA 16802, USA
Abstract
We have found that adding a proper amount of water can dramatically improve conversion of a sub-bituminous coal in solvent-freeliquefaction under at 350C using ammonium tetrathiomolybdate (ATTM) as precursor to dispersed MoS2 catalyst H2 pressure. However,
adding water to catalytic reactions at 400C decreased coal conversion, although water addition to the non-catalytic runs was slightly
beneficial at this temperature. We further examined the effect of water in solvent-mediated runs in addition to dry tests and explored a
temperature-programmed liquefaction (TPL) procedure to take advantage of the synergetic effect between water and dispersed Mo catalyst
precursor at low temperatures for more efficient coal conversion. The TPL using ATTM with added water at 350 C, followed by water
removal and subsequent reaction at 400C gave good coal conversion and oil yield. Model reactions of dinaphthyl ether (DNE) were also
carried out to clarify the effect of water. Addition of water to ATTM substantially enhanced DNE conversion at 350 C. The combination of
data from one-step and two-step tests of DNE and coal at 350400C revealed that water results in highly active MoS2 catalyst in situ
generated at 350C, but water does not promote the catalytic function or reaction once an active catalyst is generated. Using ATTM coupled
with water addition and removal and temperature-programming may be an effective strategy for developing a better coal conversion process
using dispersed catalysts. 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Coal; Liquefaction; Catalyst; Molybdenum sulfide; Water; Synergetic effect; Temperature-programmed liquefaction
1. Introduction
Research and development on conversion of coal to clean
liquid fuels and chemical feedstocks are important for effec-
tive resource utilization and for secure supply of liquid
transportation fuels and one- to four-ring aromatic chemi-
cals in the 21st century [17]. The conversion may be
realized by either direct or indirect liquefaction routes [5
7]; within the direct route, coal conversion can be carried
out in the absence or presence of a process vehicle solvent,
or in the coprocessing mode together with petroleum resi-
dues or waste plastics or waste tires. Liquefaction of coal byhydrogenation at high temperatures under high pressures
had itstechnological root in Germany [8,9]. Thereis no funda-
mental difference in chemical processing principals between
direct coal liquefaction and coal/petroleum coprocessing.
Modern petroleum hydrotreating catalysts such as sulfided
CoMo and NiMo supported on alumina originated from
early work on catalytic hydrogenation of coal and coal-
derived liquids [9]. The general directions of approaches
for converting heavy materials with lower hydrogen
contents are to increase the hydrogen-to-carbon ratio by
either hydrogen addition or carbon rejection. Direct lique-
faction of coal by hydrogenation is also called hydrolique-
faction.
Scheme 1 is a general reaction model for coal liquefaction
(TF: thermal fragmentation; HD: hydrogen donation by
hydrogens in coal, vehicle and gas-phase H2; PRIOM:promptly re-crosslinked or repolymerized (fragments-
derived) insoluble organic materials; PreAsp: preasphal-
tene; Asp: asphaltene, Oil: oils are hexane- or pentane-solu-
ble products including light distillates). It shows a general
scheme that conceptually illustrates the sequential, parallel
and retrogressive reactions encountered in direct liquefac-
tion [10,11]. Direct liquefaction proceeds through two
loosely defined stages, dissolution or primary liquefaction
in the first stage and upgrading of primary products in the
second stage to produce liquids that are like synthetic crude
oils. Primary liquefaction involves thermal fragmentation
Fuel 79 (2000) 249261
0016-2361/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved.
PII: S0016-2361(99) 00159-3
www.elsevier.com/locate/fuel
* Corresponding author. Tel.: 1-814-863-4466; fax: 1-814-865-3075.
E-mail address: [email protected] (C. Song).1 The paper is based on an invited lecture given by this author at the 1999
International Symposium on Fundamentals for Innovative Coal Utilization,
24 February 1999, Sapporo, Japan.2 Present address: Center for Cooperative Research, Toyama University,
Toyama 930, Japan.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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(TF) of coal macromolecular structure to produce free radi-
cals followed by hydrogen donation (HD) by hydroaromatic
or other hydrogen-donating species in coal itself, in vehicle
solvent, and in gas-phase H2 which leads to products
consisting of so-called preasphaltene, asphaltene and oil
along with C1C4 hydrocarbons and inorganic gases. Preas-
phaltene and asphaltene are often called liquefied
products but they are solids at ambient temperatures. Theincorporation of PRIOM (promptly re-crosslinked (frag-
ments-derived) insoluble organic materials) in the reaction
model is conceptually important, especially for early stage
of coal liquefaction because retrogressive reactions can
occur to a significant extent [1013]. We also observed
evidence of retrogressive reactions even in the presence of
catalyst during coal liquefaction [14]. It is the reactive
nature of the solid coal organic matrix that demands the
catalyst to be effective at the onset of thermal fragmentation
reactions, otherwise the reactive fragments (radicals) will
seek self-stabilization by cross-linking reactions leading to
PRIOM. This is different from most other catalytic hydro-genation processes, where the reactants are not converted
unless they are activated by interaction with the catalytic
sites.
The present work concerns direct coal liquefaction using
a dispersed molybdenum sulfide catalyst precursor, which
will generate catalytically active molybdenum sulfide mate-
rial in situ under the reaction conditions. The precursor may
be dispersed on coal surface or added to the reaction
mixture, and it may be a water-soluble or an oil-soluble
compound. The historical development and advantages of
dispersed catalysts for coal liquefaction have been well
documented by Derbyshire [15,16] and Weller [17,18].
The term dispersed catalyst used in the research area ofcoal liquefaction generally refers to the catalytic material
employed as particles dispersed on coal surface or dispersed
in the feed mixture, without using conventional porous
support. The advantage of dispersed catalysts is largely
due to their intimate contact with the surface of coal parti-
cles, which facilitates the activation and transfer of hydro-
gen to the coal-derived fragments and reactive sites. Since
most active catalysts of interest (e.g. MoS2) are insoluble in
common solvents, the desire to achieve better dispersion
leads to the strategy of using a soluble precursor that can
be dispersed onto coal surface from its solution, or dispersed
in the coal/vehicle feed mixture. The precursor may not be
active itself, but it is transformed at elevated temperatures
into an active catalyst. Sulfided molybdenum is a typical
hydrogenation catalyst.
Extensive prior studies at the Pennsylvania State Univer-
sity [1932], at Federal Energy Technology Center of US
DOE [33 38] and at many other research organizations
have demonstrated the potential of a dispersed molybdenum
catalyst for coal liquefaction. In many cases, the catalyst
was impregnated on coal as a precursor salt such as ammo-
nium molybdate or sulfided ammonium molybdate, which
decomposes upon heating to higher temperatures to form
MoS2 [39] and thus disperses MoS2 on coal. These previous
investigations have demonstrated that using dispersed
molybdenum catalyst can significantly improve coal
conversion at relatively lower temperatures. In the tempera-
ture-staged liquefaction, conducting the reaction using
sulfided molybdenum at low-temperature leads to higher
oil yield upon reaction at high temperature, without remark-
able increase of hydrocarbon gas [15,16]. Spectroscopiccharacterization of residues from liquefaction of Blind
Canyon bituminous coal (at 350 or 400C) using dispersed
Mo and Fe catalysts (that were introduced onto coal by
impregnation) has revealed that the metallic species have
fully penetrated the coal particle [4042]. Early pilot plant
studies in the late 1970s at Dow Chemicals [43] used a
dispersed, water-soluble molybdenum compound which is
converted to sulfide in situ by reaction with sulfur initially
present in coal. Recent pilot plant tests in the 1990s at
Wilsonville [4447] and at HRI [48,49] have also demon-
strated that the use of dispersed catalyst can be superior to
supported catalyst for primary liquefaction (dissolution) ofcoal, particularly low-rank coals such as subbituminous
coals and lignites.
It is well known that water or steam deactivates hydro-
treating catalysts, such as Mo-based catalysts, under
conventional processing conditions. For coal liquefaction
using dispersed catalysts, drying after impregnation of cata-
lyst or precursor salt has been a standard procedure [19
28,3236] since the pioneering work of Weller and Pelipetz
in 1951 on dispersed catalysts [50]. It was demonstrated that
the drying conditions after impregnation of catalyst precur-
sor were influential for liquefaction of subbituminous and
bituminous coals at 400C and freeze-drying gives better
results than thermal drying [20]. Several groups havereported on the negative impacts of water addition in cata-
lytic coal liquefaction in that the presence of water led to
decrease in coal conversion or oil yield [33,51,52].
Recently, for liquefaction at a temperature (350C) lower
than those used in the previous studies mentioned earlier, we
accidentally discovered a surprisingly strong promoting
effect of water addition on catalytic conversion of two US
sub-bituminous coals using in situ generated Mo sulfide
catalyst from ammonium tetrathiomolybdate [53]. Our
work on the water effect in catalytic reactions was motivated
by some intriguing observations in our previous study on the
C. Song et al. / Fuel 79 (2000) 249261250
Scheme 1.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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influence of pre-drying of coal on its catalytic conversion or
pretreatment at low temperatures [30,54]. After we
observed the unusual, synergetic effect between ATTM
and water for coal conversion at low temperatures, we
conducted liquefaction of several coals using two different
Mo catalyst precursors, water-soluble ammonium tetrathio-
molybdate [5356] and oil-soluble Molyvan L [57].
In the present paper, we report the detailed results on the
effect of water in solvent-mediated runs in addition to
solvent-free dry tests. Using water and dispersed catalyst
precursor together could dramatically improve coal conver-
sion without any organic solvents at temperatures (325375C) that are much lower than those used in conventional
processes (400450C). However, adding water to catalytic
reactions at 400450C range decreased coal conversion,
although water addition to the non-catalytic runs was
slightly beneficial in this high temperature range. We also
explored a temperature-programmed liquefaction procedure
to take advantage of the synergetic effect between water and
dispersed Mo catalyst precursor at low temperatures for
more efficient coal conversion. Further, we conducted
some model compound reactions for understanding the
promotional effect of water.
2. Experimental
Wyodak sub-bituminous coal from DOE/Penn State Coal
Sample Bank (DECS-8) was used. It was collected in June
1990, ground to 60 mesh (sieve opening: 250 mm)
and stored under argon atmosphere in heat-sealed, argon-
filled laminated foil bags consisting of three layers. This
coal contains 32.4% volatile matter, 29.3% fixed carbon,
9.9% ash and 28.4% moisture, on as-received basis;
75.8% C, 5.2% H, 1.0% N, 0.5% S and 17.5% O, on
dmmf basis. Drying of the coal was done in a vacuum
oven (VD at 100C for 2 h). The vacuum-dried coal was
used in the liquefaction tests unless otherwise mentioned.
In selected tests, fresh raw coal and the coal pre-dried in the
presence of air (AD at 100C for 2 h) were also used for
comparison.
Reagent grade ammonium tetrathiomolybdate (ATTM,
from Aldrich with 99.97% purity) was used as the precursor
for the dispersed molybdenum sulfide catalyst. ATTM
[(NH4)2MoS4] was dispersed onto the fresh raw coal or
dried coal (1 wt% Mo on dmmf basis) by incipient wetness
impregnation (IWI) method from the aqueous solution. In a
typical IWI operation, the solution of the precursor ATTMwas intermittently added dropwise to the coal in a 100 ml
beaker, in such a fashion that the wet spots over the coal
particles do not touch each other, followed by manual stir-
ring with a glass rod until all signs of wetness disappeared.
In order to keep the metal loading at a constant level on
different coal samples, we first estimated the incipient
wetness volume prior to the catalyst impregnation, which
means the total volume of the solvent needed to reach the
point of incipient wetness: the point when the solution drops
begin to remain on the external surface of the coal. The
impregnated or the raw coal samples were dried in a vacuum
oven at 100C for 2 h before use.
Liquefaction was carried out using 4 g coal with 4 gsolvent or without any solvent in 25 ml horizontal micro-
autoclave reactors at 350 or 400C for 30 min (or tempera-
ture-programmed) under an initial H2 pressure of 6.9 MPa.
Agitation was provided by vertical shaking at about
240 strokes/min. Selected tests were conducted at other
temperatures in the range of 325450C. For the experi-
ments with added water, the weight ratio of water to
dmmf coal was kept at 0.46. The gaseous products were
collected for analysis by GC with FID and TCD. The liquid
and solid contents of the reactor were placed into a tared
ceramic thimble and separated into oil, asphaltene and
C. Song et al. / Fuel 79 (2000) 249261 251
Table 1
Effects of water addition on liquefaction of Wyodak coal at 350 C for 30 min
Catalyst (ATTM) ATTM ATTM ATTM ATTM ATTM ATTM a
Solvent 1-MN 1-MN Tetralin Tetralin
H2O addition Added Added Added Added Orig. H2O
Conversion (dmmf wt%) 14.5 22.5 26.7 66.5 31.1 56.0 36.4 62.9 25.0
Preasphaltene 4.5 7.6 7.2 25.1 12.3 21.6 10.6 22.0 9.1
Asphaltene 2.6 2.3 4.7 21.6 10.1 13.2 12.9 13.8 2.8Oil 3.5 5.4 10.3 13.3 6.1 15.4 10.2 20.8 5.4
Gases 3.9b (4.93)c 7.4 (8.64) 3.0 (2.78) 6.5 (9.20) 2.6 (3.7) 5.8 (10.39) 3.0 (2.9) 6.2 (8.96) 7.7 (9.52)
C1C4 0.18 0.25 0.29 0.46 0.25 0.35 0.28 0.35 0.25
CO 0.20 0.12 0.19 0.04 0.11 0.05 0.13 0.04 0.37
CO2 4.30 8.27 2.30 8.70 3.37 9.99 2.58 8.57 8.90
H consumption (dmmf wt%)
H2 gas 0.22 0.44 1.35 1.70 1.00 1.02 1.35 1.37 0.72
Tetralin 0.08 0.22
a Fresh raw coal was used without predrying in vacuum.b The gas yields determined by weighing the micro-reactor before reaction and after releasing the gaseous products.c The figures in parenthesis are the gas yields determined by GC analysis.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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8/7/2019 catalisis heterogenea licuefaccion dle carbon
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solvents. These results reveal that using ATTM and water
together has a strong synergetic effect on coal conversion at
350C, regardless of the presence or absence of a solvent.
The addition of water caused substantial increase in CO2yields both in solvent-free and solvent-mediated runs. As
shown in Fig. 5, CO2 yield increased and CO yield
decreased upon water addition. According to the WGS reac-
tion (Eq. (1)), the increased amount of CO2 should be 1.57
times the decreased amount of CO (MW ratio:
44=28 1:57). However, when water was added to the cata-
lytic and non-catalytic reaction, CO2 yield increased from
2.34.3 wt% to 8.39.9 wt% on a dmmf basis, whereas theCO yield decreased from about 0.2 to about 0.1 wt%. The
same trends can be observed for many other tests involving
water addition, as illustrated in Fig. 6. Apparently, the
majority of enhanced CO2 yield was caused by chemical
interactions between water and the species in coal or coal
products, not by the well-known WGS. It is possible that
part of the CO2 is due to enhanced decarboxylation of
carboxylic acids (Eq. (2)) in the presence of H2O, without
causing retrogressive cross-linking. The enhanced conver-
sion of carboxylic acids was observed in hydrothermal reac-
tions by Siskin and coworkers [58,59]. Another possibility
for enhanced CO2 formation is the reaction between water
and carbonyl groups (Eq. (3)) in the coal to produce CO2.
The formation of CO2 from water and carbonyl groups was
also suggested by Lewan [60] for hydrous pyrolysis of shale.
CO H2O CO2 H2 1
RCOOH RH CO2 2
RCOR H H2O RH CO2 RHH
R; R H aryl or alkyl3
ROR H H2O ROH R HOH R; R H aryl or alkyl
4
It is clear that the observed promoting effect of water
on coal conversion in the catalytic conversion is far above
and beyond the effect of water in non-catalytic hydrother-
mal reaction. The beneficial effect of hydrothermal
pretreatment of coal has been reported by Graf and
Brandes [61] and by Bienkowski et al. [62]. The hydro-
thermal reactions of coal and possible involvement of
mineral matters have been reported by Ross et al. [63].
The use of carbon monoxide and water together for coal
liquefaction has been reported in previous studies follow-
ing the early work by Appell et al. [64]. However, the
present work involves no added CO; the CO produced
from the coal is too small to account for the enhanced
conversion (by water gas shift reaction).
C. Song et al. / Fuel 79 (2000) 249261 253
Fig. 3. Effect of water addition on liquefaction of DECS-8 Wyodak coal at
350C for 30 min in the presence of 1-methylnaphthalene (non-donor)
solvent.
Fig. 4. Effect of water addition on liquefaction of DECS-8 Wyodak coal at
350C for 30 min in the presence of tetrahydronaphthalene (H-donor)
solvent.
Fig. 5. Effect of water addition on gas formation during liquefaction of
DECS-8 Wyodak coal at 350C for 30 min without any organic solvent
(vacuum-dried coal was used for both non-catalytic and catalytic runs).
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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To clarify the effects of dispersed catalyst and water
on chemical composition of products, we have
performed two-dimensional HPLC analysis of the oils
from various liquefaction reactions using a normal-
phase column [65]. The HPLC results revealed that
the oils from catalytic liquefaction with added water
contain more phenolic compounds [66]. This suggeststhat water participates in the reaction leading to phenols
(Eq. (4)). Supporting evidence for Eq. (4). can also be
found in previous studies by Townsend and Klein [67]
on hydrothermal reactions of dibenzylether with water
at 374C and by Siskin and Katritzky [59] on diary-
lether with water at 315C.
3.2. Effect of water addition on runs at 400C
Table 2 shows the results for non-catalytic and catalytic
runs using ATTM with and without added water at 400C
and Fig. 7 illustrates the effect of water and ATTM. In the
absence of added water, use of ATTM improved coal
conversion substantially, which is manifested by enhancedoil and asphaltene formation. These increases are also
accompanied by enhanced H2 gas consumption. Compared
to the runs at 350C, the positive effect of water addition to
the non-catalytic run becomes much less, but the positive
impact of using ATTM becomes much more remarkable.
The use of ATTM for reaction at 400C afforded a high
C. Song et al. / Fuel 79 (2000) 249261254
Fig. 6. Effect of water addition on gas formation during liquefaction of DECS-8 Wyodak coal at 350C for 30 min using ATTM loaded on the fresh raw coal
(Raw), vacuum-dried coal (VD) and air-dried coal (AD) without any organic solvent. Cat means catalyst precursor ATTM.
Table 2
Effect of water addition on catalytic liquefaction of Wyodak coal at 400C for 30 min
Catalyst (ATTM) ATTM ATTM ATTM ATTM ATTM ATTM
Solvent 1-MN 1-MN Tetralin Tetralin
H2O addition Added Added Added Added
Conversion (dmmf wt%) 27.4 35.4 85.4 62.1 70.9 61.8 83.6 80.3Preasphaltene 10.1 4.8 12.4 12.0 16.9 13.3 22.6 21.7
Asphaltene 1.7 2.2 19.7 10.5 12.8 10.7 16.9 14.9
Oil 9.3 16.1 45.8 28.2 34.0 28.1 36.4 34.0
Gas 8.5a (7.6)b 12.3 (12.54) 7.5 (10.1) 11.4 (11.23) 7.3 (9.91) 9.7 (12.82) 7.7 (9.74) 9.7 (12.73)
C1C4 0.85 1.07 2.61 1.64 1.86 1.49 1.86 1.56
CO 0.41 0.21 0.10 0.02 0.18 0.02 0.17 0.03
CO2 6.35 11.26 7.39 9.57 7.87 11.31 7.71 11.14
H consumption (dmmf wt%)
H2 gas 0.95 0.68 2.80 1.38 1.81 0.90 1.75 0.72
Tetralin 0.91 1.16
a The gas yields determined by weighing the microreactor before reaction and after releasing the gaseous products.b The figures in parenthesis are the gas yields determined by GC and volumetric analyses.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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coal conversion, 85.4 wt%, and a high oil yield, 45.8 wt%.However, addition of water to the catalytic run decreased
coal conversion (to 62.1 wt%) and oil yield (to 28.2 wt%).
This is in distinct contrast to the trends for corresponding
runs at 350C. The negative effect of water addition on
solvent-free catalytic reaction at 400C is in agreement
with common knowledge that water is detrimental to cata-
lytic hydroprocessing. Similar trends can be observed from
comparing the catalytic tests in 1-MN (Fig. 8) with and
without water. However, when tetralin (Fig. 9) is present,
the negative impact of water on catalytic reaction at 400C
is reduced significantly. This is due, at least in part, to the
hydrogen-donating ability of the hydroaromatic ring intetralin to reactive fragments such as radicals. It is interest-
ing to note from the hydrogen consumption data in Table 2
that the contribution from H2 gas is more than that from
tetralin in the catalytic run without added water, but tetralin
contributes more to hydrogen transfer in the presence of
added water, supporting our explanation of the trends in
Fig. 9.
Fig. 10 shows the effect of water on gas formation at
400C. The trends observed from Fig. 8 are very similar
to those from Fig. 10, indicating that water addition signifi-
cantly promotes CO2 formation at both 350 and 400C,
regardless of its effect on coal conversion. In general, we
have observed that water addition or the original moisture in
coal enhances the CO2 formation.
3.3. Influence of temperature in the range 325450C
The results at 350 and 400C show that temperature is an
important factor influencing both the water effect and coal
conversion. We also expanded the range of temperatures to
325450C. Fig. 11 shows the effect of reaction temperature
on conversion of Wyodak coal with impregnated ATTM in
the presence and absence of added water without using
organic solvent. The advantage of the promoting effect
can be seen clearly by comparison with the catalytic runs
without added water in Fig. 11. Apparently the addition of
water to catalytic runs strongly promote coal conversion at
low temperatures, reaching the maxim benefit at 375C.
Further increasing reaction temperature above 375C caused
decrease in coal conversion in 400450C range. It may be
that water has two opposing effects on the reaction system,
depending on temperature. For the change in water property
with temperature, Fig. 12 shows the negative logarithm of
the ion product of water vs. temperature at atmospheric
pressure and under elevated pressures, which is based on
the study by Marshall and Franck [68]. It appears that there
is a rapid change near the critical point of water(Tc 374C; Pc 218 atm). It is interesting to note that
optimum temperature for catalytic tests with ATTM and
water also appears to be around this temperature (Fig. 11).
One of the effect maybe that water can help to disperse the
catalyst precursor molecules and this is also consistent with
our model tests described later.
The conversion in catalytic runs without water increases
with reaction temperature up to 400C. The further increases
in temperature to 425 and 450C resulted in decreases in
coal conversion. This is an indication that the rate of radical
formation exceeded the rate of radical capping by hydroge-
nation (Scheme 1) and in fact the H2 consumption did notincrease any further when the temperature was increased
above 400C, as shown in Fig. 13. These results indicate
the occurrence of retrogressive reactions even in the
presence of a dispersed Mo catalyst under H2 pressure
under the conditions used. We have discussed in separate
papers on retorogressive reactions in thermal reactions and
in catalytic reactions of coal.
3.4. Temperature-programmed liquefaction (TPL)
Based on the above results, it is of interest to examine
whether we can intentionally enhance the overall liquefaction
C. Song et al. / Fuel 79 (2000) 249261 255
Fig. 7. Effect of water addition on liquefaction of DECS-8 Wyodak coal at
400C for 30 min without any organic solvent.
Fig. 8. Effect of water addition on liquefaction of DECS-8 Wyodak coal at
400C for 30 min in the presence of 1-methylnaphthalene (non-donor)
solvent.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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efficiency by utilizing the strong-promoting effect of water
on ATTM-loaded coal at low temperatures. Therefore, we
conducted several exploratory experiments of temperature-
programmed liquefaction (TPL). Table 3 shows the results.
The TPL runs shown in the first five columns of Table 3
involve rapid heat up to 350
C, holding at 350
C for 30 min,followed by heat up to 400C and a final holding time of
30 min at 400C. In the presence of added water throughout
the reaction process, it appears to be beneficial to use ATTM
and the H-donor solvent together. However, the overall
conversion levels and oil yields are not more than the
single-stage 400C runs shown in Table 2 without added
water. This is likely due to the negative effect of water on
the catalytic reactions or negative effect of water on in situ
generated Mo sulfide catalyst.
Consequently, we examined the effect of hot water
removal as the inter-stage separation. No solvent was usedin this batch process. The sixth and seventh columns of
Table 3 give the results. It is clear that hot water removal
C. Song et al. / Fuel 79 (2000) 249261256
Fig. 9. Effect of water addition on liquefaction of DECS-8 Wyodak coal at 400C for 30 min in the presence of tetrahydronaphthalene (H-donor) solvent.
Fig. 10. Effect of water addition on gas formation during liquefaction of
DECS-8 Wyodak coal at 400C for 30 min without any organic solvent.
Fig. 11. Effect of reaction temperature on conversion of DECS-8 Wyodak
coal with ATTM in the presence and absence of added water without using
organic solvent.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
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after the reaction with ATTM at 350C is very beneficial to
the subsequent coal conversion and oil formation at 400C.
From process consideration, it is also beneficial to have
an inter-stage separation to remove water after the first
stage. Figs. 14 and 15 present the system timepressure
profiles for the batch reactors during heat-up and holding.
It is clear from comparing non-catalytic and catalytic runs
that H2 uptake begin to occur during the heat-up and the
early stage of reactions at the given temperatures. The use of
water leads to higher system pressure both in catalytic and
non-catalytic reactions. The non-catalytic system pressure
profile of the reactor containing vacuum-dried coal with
added water (in Fig. 14) is similar to that with fresh raw
coal charged to the reactor without predrying during heat-up
and holding at 350C. If the system pressure is fixed, then
the partial pressure of H2 would decrease due to water addi-
tion. The more rapid pressure drop due to catalyst use at
400C in the initial stage (Fig. 15) compared to 350C (Fig.
14) indicates a higher demand of the system for H2 due to
faster thermal fragmentation of coal organic matrix athigher temperature. However, the presence of water at
both low and high temperature causes the pressure to
increase in the batch reactions. This means that in the
continuous flow runs the H2 partial pressure would be
lower due to the steam partial pressure at the constant
total pressure. Since water addition dramatically enhances
the catalytic conversion at lower temperatures (325375C)
but has no positive impact on catalytic reactions at higher
temperatures (400450C), inter-stage water removal
should ensure a higher H2 partial pressure for reactions at
higher temperature. One added benefit of the inter-stage
water gas/liquid separation may be that this water streammay contain more dissolved phenols that can be separated to
make phenolic chemicals [3].
Based on the above results, we propose a new process
characterized by temperature-programmed liquefaction
using dispersed Mo catalyst precursor together with a proper
amount of water in the first stage at 325375C, inter-stage
hot removal of water and other gases, followed by second
stage reaction at 400 440C. We have also performed GC
MS and some HPLC analyses of the oil products. The use of
ATTM together with water in TPL affects not only coal
conversion, but also the chemical compositions of oil
C. Song et al. / Fuel 79 (2000) 249261 257
Fig. 12. Negative logarithm of the ion product of water vs. temperature at
atmospheric and elevated pressures.
Fig. 13. Effect of reaction temperature on gas-phase H2 consumption and
conversion of DECS-8 Wyodak coal with ATTM without using organic
solvent or water.
Table 3Temperature-programmed liquefaction using ATTM and water with and without inter-stage hot water removal
Catalyst (ATTM) ATTM ATTM ATTM ATTM ATTM ATTM
Rxn solvent 1-MN 1-MN Tetralin Tetralin
1st stage temp (C) 350 350 350 350 350 350 350 400 400
H2O in 1st stage Added Added Added Added Added Added No No
Hot water removal N/A No No No No Yes Yes N/A N/A
2nd stage temperature (C) 400 400 400 400 400 400 400 350 350
H2O in 2nd stage No Yes Yes Yes Yes No No Added Added
Conversion (dmmf wt% ) 33.5 43.5 62.7 75.6 85.6 91.7 90.7 89.7 88.3
Preasphaltene 6.4 7.4 11.3 19.8 20.5 22.6 20.4 19.9 11.0
Asphaltene 2.7 5.7 13.9 13.5 19.9 18.2 18.9 14.9 24.3
Oil gases 24.4 30.4 37.5 42.2 45.2 50.9 51.4 55.0 52.9
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products, even when the oils yields are similar between runs
under different conditions.
3.5. Role of water in catalytic liquefaction by model tests
To clarify the origin of the observed strong synergetic
effect between water and ATTM for coal conversion at
350C, we conducted model compound reactions using
dinaphthyl ether (DNE). Scheme 2 (Model reactions of
DNE using ATTM with and without added water in n-C13solvent at 350C.) presents the results of DNE tests using
catalyst in situ generated from ATTM with and without
added water. DNE shows little or no conversion with
added H2O alone. The strong-promoting effect of water on
the tests using ATTM in one-step reaction is clearly seen
from high degree of CO bond cleavage, high DNE conver-
sion and tetralin yield. To see if water is involved in ATTM
activation or catalytic reaction of DNE, we performed
C. Song et al. / Fuel 79 (2000) 249261258
Fig. 14. System timepressure profiles for catalytic and non-catalytic reactions of DECS-8 Wyodak coal at 350 C in the absence and presence of added water
without organic solvent.
Fig. 15. System timepressure profiles for catalytic and non-catalytic reactions of DECS-8 Wyodak coal at 400 C in the absence and presence of added water
without organic solvent.
8/7/2019 catalisis heterogenea licuefaccion dle carbon
11/13
two-step reactions, where water was added before or after
ATTM decomposition (1st step) and water was left orremoved before the reaction of DNE (2nd step).
The combination of the one-step and two-step tests of
DNE revealed that at a low temperature of 350C, the
main role of water is to promote the formation of highly
active Mo sulfide catalyst. BET measurements showed that
the Mo sulfide generated with added water at 350C has
much higher surface area, 335 m2/g, and much higher poros-
ity, 0.85 ml/g, than the Mo sulfide from ATTM alone
(54 m2/g, 0.17 ml/g).
We also performed more detailed model compound tests
using dinaphthyl ether [69] and 4-(1-naphthylmethyl)biben-
zyl at different temperatures [70,71] and an unexpectedoutcome of clarifying the unusual observation in coal lique-
faction led us to finding a new method for preparing highly
active MoS2 catalyst [72]. It was also found that in the
model compound tests that the catalysts in situ generated
at 375C appear to be more active than those generated at
either a lower (350C) or a higher (400C) temperature [69
71].
4. Summary and conclusions
The use of ATTM with added water (for in situ generation
of Mo sulfide catalyst) can lead to substantially higher coalconversion to soluble products at relatively low tempera-
tures such as 350C. This strong promoting effect of water
addition on catalytic coal conversion at 325375C does not
depend on hydrogen-donor or non-donor solvent. Model
reactions coupled with liquefaction data suggest that better
dispersed MoS2 catalyst with higher surface area is
produced from ATTM in the presence of added water
under proper conditions. However, the use of water appears
to have a negative impact on catalytic coal conversion at
higher temperatures such as 400425C; the use of a good
hydrogen-donor solvent can alleviate this effect at higher
temperatures. The use of water also leads to enhanced
CO2 formation at either low or high temperatures, regardlessof its impact on coal conversion.
On the basis of coal conversion under different conditions
coupled with one-step and two-step tests of model
compounds, we propose a new process concept character-
ized by temperature-programmed liquefaction using
dispersed Mo catalyst precursor together with a proper
amount of water in the first stage at 325375C, inter-
stage hot removal of water and other gases, followed by
second stage reaction at 400440C under H2 pressure
[73,74]. The results from this work point to a promising
new direction for further research in catalytic conversion
of coal to liquid fuels and chemical feedstocks.While the trends observed in this study have been found
to be reproducible, it must be noted that the present results
were obtained in 25 ml micro-reactors. They should not be
compared on absolute yield basis with the data from large-
scale tests. Mass transfer conditions are different between
the micro-tubing reactors and in stirred-tank autoclave reac-
tors and the amount of coal sample used in a given reactor
system can also be influential. Care must be taken when one
tries to compare liquefaction data from different sources.
Acknowledgements
We are very grateful to Prof Harold H. Schobert for his
encouragement and support of this work and for many help-
ful discussions. We are pleased to acknowledge US DOE/
Federal Energy Technology Center for financial support of
our prior studies that led us to the present work. We wish to
thank the Ministry of Education of Japan for providing
financial support to this work in our laboratory at PSU
through a fellowship to Y.Y. on leave from Toyama Univer-
sity of Japan. We also thank Mr Ron Copenhaver for the
fabrication of the micro-reactors used in this work.
C. Song et al. / Fuel 79 (2000) 249261 259
Scheme 2.
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