catalisis heterogenea licuefaccion dle carbon

8/7/2019 catalisis heterogenea licuefaccion dle carbon

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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.


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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.


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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.


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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.


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).


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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.


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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


400C for 30 min without any organic solvent.


400C for 30 min in the presence of 1-methylnaphthalene (non-donor)

solvent.


8/13

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.


9/13

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


10/13

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.


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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References

[1] Derbyshire FJ. Chemtech 1990;20:439.

[2] Mochida I, Sakanishi K. Adv Catal 1994;40:39.

[3] Song C, Schobert HH. Fuel 1996;75:724.

[4] Song C, Schobert HH, Scaroni AW. Proceedings of the 14th Annual

International Pittsburgh Coal Conference, Taiyuan, Shanxi, China,

2327 September 1997, Paper no. 22-1.

[5] Derbyshire F, Gray D. Coal liquefaction. Ulmanns encyclopedia of

industrial chemistry, A7. Weinheim: VCH, 1986. p. 197.

[6] Farcasiu M. Liquid transportation fuels from coal. Part 1: direct lique-

faction. PETC Review, US DOE, Pittsburgh, March 1991. p. 4.

[7] Stiegel GJ. Liquid transportation fuels from coal. Part 2: indirect

liquefaction. PETC Review, US DOE, Pittsburgh, Fall 1991. p. 14.

[8] Stranges AN. Fuel Process Technol 1987;16:205.

[9] Donath EE. Fuel Process Technol 1977;1:3.

[10] Song C, Hanaoka K, Nomura M. Fuel 1989;68(3):287.

[11] Song C, Nomura M, Ono T. Am Chem Soc Div Fuel Chem Prepr

1991;36:586.

[12] DOE COLIRN Panel. Coal liquefactionsa research and develop-

ment needs assessments. DOE DE-AC01, 87ER30110, US DOE.

Final report, vols. 1 and 2, 1989.

[13] Saini AK, Coleman MM, Song C, Schobert HH. Energy & Fuels1993;7(2):328.

[14] Song C, Saini AK, Schobert HH. Coal science and technology, 24.

Amsterdam: Elsevier, 1995. p. 1215.

[15] Derbyshire F. Catalysis in coal liquefaction. IEACR/08, IEA Coal

Research, London, 1988.

[16] Derbyshire F, Hager T. Fuel 1994;73:1087.

[17] Weller SW. Coal liquefaction with molybdenum catalysts. In: Barry

HF, editor. Chemistry and uses of molybdenum, Ann Arbor, MI:

Climax Molybdenum, 1982. p. 179.

[18] Weller S. Energy & Fuels 1994;8:415.

[19] Derbyshire FJ, Davis A, Epstein M, Stansberry PG. Fuel

1986;65:1233.

[20] Derbyshire FJ, Davis A, Lin R, StansberryPG, Terrer M. Fuel Process

Technol 1986;12:127.

[21] Davis A, Derbyshire FJ, Finseth DH, Lin R, Stansberry PG, Terrer M-T. Fuel 1986;65:500.

[22] Garcia AB, Schobert HH. Fuel 1989;68:1613.

[23] Artok L, Davis A, Mitchell GD, Schobert HH. Fuel 1992;71:981.

[24] Artok L, Davis A, Mitchell GD, Schobert HH. Energy & Fuels

1993;7:67.

[25] Huang L, Song C, Schobert HH. Am Chem Soc Div Fuel Chem Prepr

1992;37:223.


1993;38:1093.


1994;39:591.

[28] Song C, Parfitt DS, Schobert HH. Catal Lett 1993;21:27.

[29] Song C, Hou L, Saini AK, Hatcher PG, Schobert HH. Fuel Process

Technol 1993;34:249.

[30] Song C, Saini AK, Schobert HH. Energy & Fuels 1994;8:301.[31] Song C, Saini AK, Schobert HH. Proceedings of the Seventh Inter-

national Coal Science Conference, Banff, Canada, 1227 September

1993, vol I, p. 291.

[32] Burgess CE, Schobert HH. Energy & Fuels 1996;10:718.

[33] Bockrath BC, Finseth DH, Illig EG. Fuel Process Technol

1986;12:175.

[34] Utz BR, Cugini AV, Frommell EA. Am Chem Soc Symp Ser

1989;437:289.

[35] Warzinski RP, Bockrath B. Energy & Fuels 1996;10:612.

[36] Ferrance JP, Warzinski RP, Bockrath B. Am Chem Soc Div Fuel

Chem Prepr 1998;43:694.

[37] Cugini AV, Rothenberger KS, Ciocco MV, Veloski GV. Energy &

Fuels 1997;11:213.

[38] Cugini AV, Rothenberger KS, Krastman D, Ciocco MV, Thompson

RL, McCreary C, Gardner TJ. Catal Today 1998;43:291.

[39] Naumann AW, Behan AS, Thorsteinson EM. In: Barry HE, Mitchell

CN, editors. Proceedings of the Fourth International Conference on

Chemistry and Uses of Molybdenum, 1982. p. 313.

[40] Sommerfeld DA, Jaturapitpornsakul J, Anderson LL, Eyring EM. Am

Chem Soc Div Fuel Chem Prepr 1992;37:749.

[41] Sommerfeld DA, Tuntawiroon W, Anderson LL, Eyring EM. Am

Chem Soc Div Fuel Chem Prepr 1993;38:211.[42] Anderson LL, Yuen WH, Jaturapitpornsakul J, Sommerfeld DA,

Eyring EM. Am Chem Soc Div Fuel Chem Prepr 1993;38:142.

[43] Moll NG, Quarderer GJ. Proceedings of the Third International

Conference on Chemistry and Uses of Molybdenum. 1923 August

1979, Ann Arbor, MI, p. 232.

[44] Lee JM, Vimalchand P, Cantrell CE, Davies OL. Proceedings of the

US DOE Liquefaction Contractors Review Conference, 2224

September 1992, US Department of Energy, Pittsburgh, p. 35.

[45] Vimalchand P, Lee JM, Davies OL, Cantrell CE. Proceedings

of the US DOE Liquefaction Contractors Review Conference,

2224 September 1992, US Department of Energy, Pittsburgh,

p. 175.

[46] Swanson A. Proceedings of the US DOE Liquefaction Contractors

Review Conference, 2224 September 1992, US Department of

Energy, Pittsburgh, p. 107.[47] Swanson A. Am Chem Soc Div Fuel Chem Prepr Pap 1992;37:

149.

[48] Comolli AG, Lee LK, Pradhan VR, Stalzer RH. Proceedings of the

Coal Liquefaction and Gas Conversion Contractors Review Confer-

ence, US Department of Energy, Pittsburgh, 78 September 1994,

p. 19.

[49] Lee LK, Pradhan VR, Stalzer RH, Johanson ES, Comolli AG.

Proceedings of the Coal Liquefaction and Gas Conversion Contrac-

tors Review Conference, US Department of Energy, Pittsburgh, 78

September 1994. p. 33.

[50] Weller S, Pelipetz MG. Ind Engng Chem Chem 1951;43:1243.

[51] Ruether JA, Mima JA, Kornosky RM, Ha BC. Energy & Fuels

1987;1:198.

[52] Kamiya Y, Nobusawa T, Futamura S. Fuel Process Technol

1988;18:1.

[53] Song C, Saini AK. Energy & Fuels 1995;9:188.

[54] Song C, Saini AK, Schobert HH. Am Chem Soc Div Fuel Chem Prepr

1993;38:1031.

[55] Song C. Energia, University of Kentucky, vol 6, 1995. p. 1.

[56] Byrne R, Song C. Am Chem Soc Div Fuel Chem Prepr 1995;40:

537.

[57] Song C, Saini AK, McConnie J. Coal Sci Technol 1995;24:1391.

[58] Siskin M, Brons G, Vaughn SN, Katritzky AR, Balasubramanian M.

Energy & Fuels 1990;4:488.

[59] Siskin M, Katritzky AR. Science 1991;254:231.

[60] Lewan MD. Am Chem Soc Div Fuel Chem Prepr 1992;37(4):

1643.

[61] Graf RA, Brandes SD. Energy & Fuels 1987;1:84.

[62] Bienkowski PR, Narayan R, Greenkorn RA, Chao K-C. Ind Engng

Chem Res 1987;26:206.

[63] Ross DS, Jayaweera I, Hoogwater S. Am Chem Soc Div Petrol Chem

Prepr 1994;39:353.

[64] Appell HR, Wender I, Miller RD. Chem Ind 1969;47:1703.

[65] Song C, Saini AK. Am Chem Soc Div Fuel Chem Prepr 1994;

39:796.

[66] Song C, Saini AK. Am Chem Soc Div Fuel Chem Prepr

1994;39:1103.

[67] Townsend SH, Klein MT. Fuel 1985;64:635.

[68] Marshall WL, Franck EU. J Phys Chem Ref Data 1981;10:295.

[69] Yoneyama Y, Song C. Am Chem Soc Div Fuel Chem Prepr

1997;42:52.

[70] Yoneyama Y, Song C, Reddy KM. Am Chem Soc Div Petrol Chem

Prepr 1997;42:550.

C. Song et al. / Fuel 79 (2000) 249261260


13/13

[71] Yoneyama Y, Song C. Catal Today 1999;50:19.

[72] Song C, Reddy KM, Yoneyama Y. Am Chem Soc Div Petrol Chem

Prepr 1998;43:563.

[73] Song C, Saini AK, Yoneyama Y. Proceedings of the 14th Annual

International Pittsburgh Coal Conference, Taiyuan, Shanxi, China,

2327 September 1997, Paper no. 8-4.

[74] Vijay P, Song C, Schobert HH. Am Chem Soc Div Fuel Chem Prepr

1995;40:542.

C. Song et al. / Fuel 79 (2000) 249261 261

catalisis heterogenea licuefaccion dle carbon

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