Catalytic Liquefaction of Coal With Supercritical Water CO Solvent Media

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Catalytic liquefaction of coal with

supercritical water/CO/solvent media

L. A. Amestica” and E. E. Wolf

Chemic al Engineering Departm ent, University of Notre Dame, Notre Dame, IN 46556,

USA

Received 11 Septemb er 7985; revised 5 May 1986)

This paper describes studies of the catalytic activity of cobalt molybdenum sulphide, cobalt molybdenum

oxide, iron sulphate, iron acetate dibasic and H,S during the reaction between supercritical CO and water,

and during liquefaction of coal using supercritical CO-water-solvent mixtures. The kinetics of the water gas

shift reaction was studied first and was found to be first order in all the catalysts studied. The activity of the

catalysts decreased in the following order: cobalt molybdenum sulphide > cobalt molybdenum oxide > iron

salts. The presence of toluene, tetralin, and THQ decreased the CO conversion on the cobalt catalysts but

increased CO conversion in the presence of iron salts catalysts. Moderate coal conversion of toluene soluble

products (25 x-35 %) were obtained in the presence of supercritical water and water/CO mixtures. Addition

of organic solvents to a supercritical water/CO medium increased conversion of toluene soluble products to

7&80x for THQ, to 50-60x for tetralin, and to 3540% for toluene. Addition of H,S to the

solvent/water/CO medium increased conversion to toluene soluble products even further. In the presence of

H,S/solvent/water/CO, the presence of catalysts had only a minor effect on coal conversion and were not

required to achieve high coal conversions. The optimum operating conditions for an Illinois No. 6 coal were

obtained using a H,S/THQ/CO/water medium at 3600 psi, and 400°C. Higher conversions were attained

with a subbituminous Wyodak coal. These studies clearly demonstrate that high conversions to soluble

products can be attained using a supercritical water/CO/solvent medium.

Keywords: liquefaction of coal; catalysis; kinetics)

Attention has been given lately to coal liquefaction

processes using the water gas shift reaction (WGS) to

provide

n

situ hydrogen generation’ -4. Studies of the

liquefaction of different types of coals in water/CO

medium have shown that conversion decreases with

increasing coal rank5y6. During steam/CO coal

liquefaction, the presence of organic solvents such as

creosote oil, phenanthrene, naphthol and oil fraction,

decreases the rate of the water gas shift reaction6, but

increases the rate of coal conversion by dispersing and

dissolving the coal derived molecules3y6.

The catalysts used in steam/CO coal liquefaction must

catalyse the WGS reaction and at the same time promote

coal liquefaction. Basic salts, alkali carbonates, and alkali

hydroxides, catalyse the WGS reaction295*7 and increase

the rate of solvolysis during steam/CO coal liquefaction‘j.

Supported cobalt molybdenum (CoMo) oxide catalysts

exhibit a catalytic activity similar to the alkali salts

towards the WGS reaction, as well as towards the

hydrogenation of several coal model compounds in a

steam/CO reaction medium. However, CoMo oxide

supported catalysts promoted with alkali salts, have not

exhibited a synergistic effect during liquefaction of coal in

the presence of CO/H, atmosphere’.

The effect of the operating variables during steam/CO

liquefaction depends on the specific solvent/catalyst

combination used. In general, coal conversion increases

with temperatures in the range 370-450”C4. Appell and

*

Departamento de Ingenieria Quimica, Universidad de Chile, Casilla

2777 Santiago, Chile

OOlf&2361/86/09122&07 3.00

‘0 1986 Butterworth & Co. (Publishers) Ltd.

1226

FUEL, 1986, Vol 65, September

Wender3 report that coal conversion increases with CO

partial pressure, whereas Baldwin

et ~1.~

ound no such

effect. Ross

et al.’

reports that coal conversion is higher in

the presence of H,O/CO than in H&O, moreover these

authors report that coal conversion follows the rate of H,

production.

Several catalysts which have potential for catalysing

both the WGS reaction and coal liquefaction have not yet

been studied. The activity of H,S in coal liquefaction9-‘3,

and its synergistic effect on iron catalysts have been

reported in the literature’4*‘5. It has been postulated that

the formation of a non-stoichiometric iron sulphate

containing ion vacancies, is responsible for the activity of

iron/H,S during coal liquefaction. The formation of ion

vacancies induced by H,S has been reported to affect the

hydrogenolysis activity of CoMo catalysts’ 3 -

“.

Furthermore Abdel-Baset and Ratcliffe” have reported

that, in the absence of hydrogen donor solvents, coal

conversion is higher in H,S/CO than in H,O/CO

atmospheres. Clearly, H,S can affect the CoMo and iron

catalysed coal liquefaction in H,O/CO/solvent media.

Catalytic liquefaction at supercritical conditions have

been previously studied in our laboratory in the presence

of tetralin and CoMo sulphided catalysts18*‘9.

Supercritical conditions enhance the solubility and

diffusivity of the solvent, and minimize mass transfer

effects by operating in a single phase system. The

objective of this work is to investigate the catalytic effect

of heterogeneous and homogeneous catalysts during

steam/CO/solvent coal liquefaction initially at supercriti-

cal conditions. As reaction occurs, the fluid phase



Catalytic liquefaction of coal: L. A. Amestica and E. E. Wolf

composition is modified by the presence of the coal

derived species which may modify the phase behaviour of

the mixture. Thus, during reaction the system may be

pseudo-supercritical rather than completely supercritical.

The catalysts and solvents investigated are supported

CoMo sulphide, iron sulphate, iron acetate, dibasic, and

H,S, in the presence of toluene, tetralin, and THQ as

organic solvents. The activity of these catalysts and the

effect of the solvents towards the WGS reaction kinetics

was first studied, followed by studies of liquefaction of an

Illinois No. 6 coal and Wyodak coals.

EXPERIMENTAL

Materials

All experiments were conducted under constant

stirring at 1200 rpm. In experiments with heterogeneous

catalysts, the pellets were loaded into a basket attached to

the reactor stirrer shaft. The CoMo catalyst was

sulphided (CoMoS) prior to reaction in a flowing H,S/H,

stream at 300°C. The CoMoS catalyst was loaded in an

amount corresponding to 100,; of the water feed, whereas

the unsupported catalysts were loaded in amounts such

that iron constituted 5 “/:,of the water feed. Iron sulphate

was dissolved in the aqueous phase (FeSO,aq) and/or

impregnated (FeSO,imp) in the coal, whereas iron

acetate hydroxide dibasic (FeAc aq) was dissolved in the

aqueous or organic phases (Fe org).

Ultimate analysis of the coals used are listed in Table I.

In experiments using organic solvents the solvent was

The Illinois No. 6 coal particle size was < 74 pm, whereas

injected into the reaction vessel when the reaction

the Wyodak coal particle sizes were < 105 pm; both coals

temperature was stabilized. The solvent was injected from

were dried in vacuum at 110°C before use. The grade of

an auxiliary vessel utilizing high pressure CO, also used to

solvents and gases used, and the catalysts characteristics inject coal in a slurry form”. The studies with solvents

are summarized in Table 2.

were conducted at 400°C for 1 h.

Procedure

I S reaction studies. Both the WGS reaction and coal

liquefaction studies were carried out in a 3OOcc batch

autoclave described elsewhere’ ‘,19. During the WGS

reaction kinetic studies, water (1 l gmole) and the catalyst

were charged into the reactor which was then sealed, leak

tested, purged and then pressurized with CO(N, or H2S)

to obtain a H,O/CO ratio of 3. After the reaction

Table 1 Ultimate analysis of Illinois No. 6 and Wyodak coals

Illinois No. 6”

(T/,)

Wyodakb

( T$)

Moisture 2.6 23.1

Carbon 66.4

50.6

Hydrogen 4.4

3.7

Sulphur 2.9 0.6

Ash

12.3 7.6

Oxygen

10.7” 13.7b

________

a Analysis supplied by Amoco Research Center. The oxygen content was

calculated by direct analysis

“Analysis supplied by Commercial Testing & Engineering Co.,

Chicago. The content of oxygen was calculated by difference

Table 2 Catalyst characteristics

Catalyst

Characteristics

CoMo oxide (CoMoO)

CoMo sulphide

(CoMoS)

Ferrous sulphate

(FeSO,)

Iron acetate

hydroxide dibasic

(FeAc(OH)J

Hydrogen sulphide

(H,S)

Amocat

1A,

particle size: l/16”

and grounded below 270~; 2.9% COO,

15.9% MOO, 172 m’/g, Ave Pore di-

ameter = 120A, bimodal pore

distribution

Obtained by sulphidation of CoMo

oxide Amocat 1 A catalyst, Particle

size l/16”

Fischer Scientific Co.

Alfa Co.

CP grade, Linde Co.

temperature was stabilized to the desired value, samples

were withdrawn at regular time intervals.

The supercritical phase was analysed by trapping 1.5 cc

sample volume and then expanding it in a 30 cc volume,

thus separating liquid and gas phases which permitted

syringe sampling of the gas phase only. 300~1 of the gas

phase were then injected into a gas chromatograph

(Varian 3700) equipped with a 8’ x l/8” column, packed

with carbosphere (177/149pm, Alltech Assoc.). To

separate CO and CO, from other gas species, the column

temperature was programmed from 50°C to 150°C at a

heating rate of 10°C min-

’ ,

using helium, flowing at

6Occ min-’

as the carrier gas. The concentrations of CO

and CO, were obtained from a calibration curve and CO

conversion was calculated as the ratio of CO, produced

divided by the sum of CO and CO,.

Coal liquefaction studies. During these studies the

following variables were held at a constant value: the

H,O/CO molar ratio = 3,

H O/coal =

1, H,O/solvent

molar ratio = 5, and CO/H,S molar ratio = 9. In a typical

experiment, the reactor was charged with one third of the

water feed, then it was closed, leak tested, and flushed

with nitrogen. The catalysts were added using the same

procedure as in the WGS reaction studies, previously

described. A slurry of water, solvent and coal, pressurized

with CO, was injected from the injection vessel into the

reactor as soon as it reached the reaction temperature.

The slurry contained the other Z/3 of the water feed, the

organic solvent, and the coal. After injection, it took

approximately 3 min for the reactor to regain its reaction

temperature of 400°C. The reaction then proceeded for

1 h, and then it was quenched by flowing water through

the reactor cooling coils. Finally upon reaching room

temperature, the gas phase was evacuated, passed

through two zinc acetate sulphur scrubbers, and its

volume was measured in a wet test meter. Gas samples

were trapped in an on line bypass sample volume for g.c.

analysis.

The slurry product from the reactor was filtered in a

Buchner funnel and the reactor walls were carefully

washed with toluene. The wash solution was filtered in the

same funnel as the slurry, and toluene was added to the

filtrate until a volumetric ratio of toluene used in the wash

and the original slurry was IO. The solution settled for

about 4 h and was then filtered again, and the wet cake


1227




TIME (min)

Figure 1 Conversion u rsus time curves for various cobalt-

molybdenum catalysts: A, blank at 400°C; 0, H,S at 400°C; x , COMO

oxide at 400°C; 0, CoMo sulphide at 240°C; CoMo sulphide/H,S

at 240°C

was Soxhlet extracted with toluene for 10 h. The toluene

insoluble fraction was dried, weighed, and its ash content

was determined. For selected runs, the toluene insoluble

fraction, was Soxhlet extracted overnight with THF to

determine the THF soluble fraction. Coal conversion,

expressed in terms of the toluene soluble or THF soluble

fraction, was calculated by subtracting the ratio of the

corresponding daf insoluble fraction and the daf coal feed,

from one.

In studies using iron salts as catalysts, the unreactive

coal fraction was calculated by subtracting from the

toluene insoluble fraction the ash content of the feed and

the weight of FeS, .i. The FeS,,, was assumed to be

formed from the reaction of H,S and the iron salts, the

stoichiometry was inferred from X-ray diffraction

analysis of the iron catalyst, after use during the WGS

studies, in the absence of coal.

RESULTS

WGS reaction ki neti cs

Prior to the WGS reaction kinetic studies, blank runs

were performed to test any possible activity of the reactor

walls, It was found that the reactor walls have some

activity

Figure I),

and that the use of a glass liner did not

decrease it significantly, consequently the experiments

were conducted without the liner.

CO conversion versus time results, obtained in the

presence of H,S, CoMo oxide, CoMo sulphide, H,S-

CoMoS and during blank runs, are shown in Figur e 1.

The CoMoS catalyst, without and with H,S, was so

active that it was necessary to lower the reaction

temperature to 240°C in order to follow the reaction

kinetics; otherwise the reaction temperature was 400°C.

The WGS reaction has been reported to follow a first

order reversible kinetics with

respect to CO

concentration20,21. The corresponding integral ex-

pression of a first order reversible kinetics in a batch

reactor is given by

ln{Xe-XJ

kt

XC

where X is the conversion, X, the CO equilibrium

conversion, and k the reaction rate constant. Figure 2

shows the kinetic data obtained during the WGS reaction

studies plotted according with Equation 1, showing

excellent agreement. The reaction rate constants,

obtained from the slope of each line, are summarized in

Table3 along with catalyst and solvent used. The rate

constants vary linearly with catalyst loading but are not

affected by changes in pressure in the range 2400 to

35OOpsi. The activation energies obtained from an

Arrhenius plot, listed in

Tabl e 3

for the studies without

solvent, clearly shows that the CoMoS catalyst is the

most active, and that H,S decreases the activation energy

when added to the reaction.

Addition of organic solvents to the reaction medium

decreases the reaction rate constants as shown in

Tabl e 3.

The relative effect of each solvent depends on the catalyst

used. For the CoMoS catalyst with and without H,S, k

decreases in the order: no solvent > toluene > tetral-

in>THQ. However, for the iron salts without H,S

present, k decreases in the order: toluene> tetralin>no

solvent, whereas in the presence of H,S, the order is

altered to no solvent = toluene > tetralin > THQ.

0

-1.00

/-\-I.50

X

’ i?

x”

-

5

-2.00

-2.50

-3.00

-3.50 /

0 20 40 60 80 100 120 140

TIME (min)

Figure 2 Correlation of the WGS kinetic data in terms of a first order

reversible kinetics. Symbols as in

Figure

1228 FUEL, 1986, Vol 65, September




Table 3 WCS rate constants and activation energies

_ _~.~__

_____.____ __

Rate

constant

at 400°C

[gcat min]

’

Catalyst

No solvent

Activation

energy

Kcal molt

’

Tetralin

Rate constant at 400°C

[gcat min]-’ x 10m3

THQ

To1

Ct)MoO

11.1 18.46

C<)MoS

1197.0” 19.33

29.9 19.7 112.6

C\,MoS-H,S

X56.6 17.00

55.0

20.2 84.8

F&O,

1.5

51.47

1.6

0.8 1.6

F&O,-H,S

10.5

21.40

4.9

3.1 5.6

Ft.Ac(OH),

2.0 29.27

1.8

1.1 3.6

FrsAc(OH),-H,S

6.9 15.00

4.1 2.4 5.5

Feed molar ratio: H,O/CO=3, CO/H,S=9; both CoMoO and CoMoS loading is IO’,,,

iron salt dissolved in water at 5 “;, iron concentration

UHxtrapolated from the data obtained at 215-26o’C

Gas chromatographic analysis of the liquids after 1 h

reaction shows that toluene did not decompose during

the reaction, however tetralin and THQ both exhibited

decomposition reactions when used with all catalysts.

About 10 % oft he tetralin reacted to toluene and decalin,

with naphthalene being detected only in the presence of

the CoMoS catalyst. The reactivity of THQ varied with

the type of catalyst used, with approximately 60x, 50%

and 10% decomposed in the presence of CoMoS, FeSO,

and FeAc respectively. Detailed identification of the

products of THQ decomposition was not possible.

( ‘oul liquejktion

The same catalysts and solvents used in the WGS

reactions studies were used during liquefaction of an

Illinois No. 6 and a Wyodak coal. In addition various

atmospheres such as

nitrogen,

water/CO, and

water/CO/H,S were also used.

Conversion of the Illinois No. 6 coal to toluene soluble

products, after 1 h of reaction and at 4Oo”C, are presented

in terms of bar diagrams in Figures 3-5. Numerical values

are summarized in

Tabled,

along with solvent, catalyst

medium and operating conditions used.

Coal conversions obtained in the presence of the

\ arious supercritical solvents-medium used, but without

catalyst

addition, are shown in Figure3. Coal

liquefaction in the supercritical media in the absence of

organic solvents (NO-SOL) exhibited relatively low

conversions ranging from about 23 to 37%. The lowest

conversion was obtained with the supercritical water/N,

medium (N) (23 %), increasing to 33 y0 with the addition

of CO (WCO) and CO/H,S (WCOHS) (37:/,).

When the two hydrogen donor solvents, tetralin and

THQ, were used in a N, medium (N-TETRA and N-

THQ), a significant increase in conversion, to about 51

and 72 /i respectively, was attained. Conversion in the

inert toluene solvent only reached 35%, even in the

presence of H,S (TOL-WHS). Conversion further

increased to about 55 and 80% when water/CO was used

with the tetralin and THQ solvents respectively. An even

further increase in conversion to about 67 and 87 “/,, was

;tttained when H,S was added to the previous mixture.

Coal liquefaction in the presence of the CoMoS

catalyst,

and the various solvents and media are

presented in

Figure 4.

The presence of the catalyst, loaded

3s 10% of the coal feed, increases conversion over the

non-catalytic runs, only by l-13.6% depending on

the

medium. As in the non-catalytic conversion,

the

90

80

70

60

t-

Z

3

a 50

2

5 40

,_

E

; 30

0

20

IO

0

L-

H s

S

W

:

MEDIA

0

i

NO- SOL

TETRA

THQ

TOL

SOLVENT

igure 3 Coal conversion to toluene soluble products in the absence of

catalysts and in the various media and solvents used: N, N,; WCO,

H,O/CO; WCOHS, H,O/CO/H,S; WHS, H,O/H,S; WNHS,

H,O/NJH,S

conversions obtained with water/CO/THQ (87 %) are

higher than with tetralin/water/CO (62%). Likewise

addition of CO/H,S further increase conversion for these

two solvents to 73 and 88% respectively. Surprisingly,

with the toluene solvent, a three fold increase in

conversion to about 60% was attained when using a

water/CO/H,S medium.


1229



Catalyt ic liquefact ion of coal: L. A. Amest ica and E. E. Wolf

90

-I

J

SO

1

90

s

i

c so

:

( I

40

90

20

10

P

I Y

:

N N

:

N N

:

II H

NLOIA

9 5

E

+ TElRI. -_I

+ TM9 --I

t_ TOL. --+ SOLVENT

Figure 4 Coal conversion to toluene soluble products in the presence

of a CoMoS catalyst. Symbols as in Figure 3

Addition of iron sulphate catalyst in the form of

aqueous solution of various concentrations, as well as

impregnated into the coal feed, and in the presence of CO

and CO/H,S, slightly decreased conversion (Table 4). The

iron acetate catalyst gave slightly higher conversion than

iron sulphate with the toluene and THQ solvents, but it

was less active with the tetralin solvent (see

Tabl e 4).

A summary of the effect of catalysts in conversion is

displayed in

Figure 5

for both the water/CO and

water/CO/H,S system. In both cases the most

active

catalyst was the CoMoS catalyst. H,S was an important

factor when toluene was used as a solvent, but its effect

decreased with the tetralin solvent, and it was almost not

relevant with the THQ solvent.

The two highest conversions of 86.9 % and 87.7 % were

attained when using THQ/water/CO/H,S without and

with the CoMoS catalyst respectively. Since the difference

was within experimental error, further optimization

studies were conducted using the THQ/water/CO/H,S

medium without catalyst. The differences in conversion

obtained when varying the pressure (260&3600 psi),

temperature (38&45oOC), THQ/coal and H&coal

ratios, were no higher than about 4%18. Consequently

they are not listed in this paper18.

The effect of reaction on conversion was also studied. It

was found that conversion after 15 min of reaction

(425°C) was higher by only 1.3 % than the value observed

after 60min. For this reason the runs reported here, all

conducted after 1 h of reaction time, are representative of

an equilibrium conversion after which, reaction time does

not play a significant role in conversion, except for minor

retroactive reactions.

Conversions obtained during liquefaction of a

subbituminous Wyodak coal using the water/CO/T’HQ/

H, medium are summarized in

Tabl e 5.

As expected,

conversions were higher than those obtained with the

Illinois No. 6 coal, ranging from about 85 to 95 % for the

toluene soluble products, and 94 to 96% for the THF

soluble products. Otherwise the effect of the variables

in conversion is similar to those observed with the Illinois

No. 6 coal.

DISCUSSION

The results obtained show that high coal conversions can

be obtained using pseudocritical water/CO/solvent

mixtures with or without added catalyst. The highest

conversion was obtained with a water/CO/THQ/H,S

combination that gave better results than each

component or their binary combination. Furthermore,

50 % more solvent was used in the pure solvent

experiment, than in the combined medium. Clearly, the

results show that the synergistic contribution of water,

CO, THQ and H,S is what produces the best results. The

complexity of the system is such that it does not permit to

ascertain unequivocally the cause of the various effects

observed. However, some rationalization of the trends

observed is presented below, based on information

available for simpler systems.

:

E 0

I s -

Y OC

ococ ococ

CATALYST

4 A

S 4 A S

4 A

f- TEk+ + ,I,‘, + T:LL-_I SOLVENT

Figure 5 Comparison of the effect of the various catalysts in

water/CO/solvent and water/CO/solvent/H,S media (blank bars):

CoMoS, sulphided cobalt molybdenum; FeAc, iron acetate; FeSO,A,

iron sulphate aqueous solution; x, N,/no catalyst; No-Cat

coal/water/CO/solvent no catalyst

1230 FUEL, 1986, Vol65, September




Table 4 Illinois No. 6 coal liquefaction conversion to toluene soluble products”

o solventb

Catalyst’

Medium”

i.4

-

Toluene

_~.

Fpsi] &)

_~

[Ppsil

Tetralin

THQ

_

5,)

Ppsil &)

_

2380 50.2

2640 71.6

2180 35.3 _

3700 55.7

3700 80.4

3700 67.1

3700 86.9

3100 21.0

2100 51.0

2100 63.0

2970 20.1

3400 52.6

3420 74.7

2800 18.1

3150 62.1

3560 87.0

3040 62.2

3340 72.9

3440 87.7

3100 25.1

_

3370 52.0

3300 82.6

3300 67.8

_ _

3700 58.8

_

_

_

2460 57.6

1900 9.2

2660 41.9

._ _

3040 18.8

3370 54.1

3370 77.7

3700 39.8

3700 61.7

3700 80.6

3340 27.5

3500 53.1

3220 72.8

3750 81.0

_ _

_

_

3700 71.6

N

N-HS

w-co

WCO-HS

N

N-W

w-co

WCO-HS

WC0

WC0

WCO-HS

WCO-HS

N

N

N-HS

WC0

WCO-HS

WC0

WC0

WC0

3620

3700

3200

3700

_

23.4

27.6

33.3

36.9

CoMoS

CoMoS

CoMoS

CoMoS

FeAc(aq)

FeAc(org)

FeAc(aq)

FcAc(org)

FeSQJaq)

FeSO,(imp)

FeSUaq)

FeSQJaq)

FeSQJaq)

FeSO,(imp)

FeSO,(aq, 3 %)

FeSOdaq, 8 )

3300

_

3700

11.5

15.6

_

_

P = pressure; X = conversion

(1Operating conditions: temperature = 400°C; reaction time= 1 h. Feed: H,O/coal= 1 (g/g); H,O/solvent = 5(gmol/gmol); H,O,ICO = 3(gmol/gmol);

CO/H,S = 9(gmol/gmol)

b No solvent, signifies runs using water without organic solvent

‘CoMoS = 10 wt % of coal feed; iron salts=5 wt % of coal feed, otherwise indicated; org=iron salt dissolved in the organic phase; aq= iron salt

dissolved in the aqueous phase; imp=iron salt impregnated on the coal

d Medium, the nomenclature stands for: N=nitrogen; W =water; CO =carbon monoxide; HS = hydrogen sulphide

Table 5 Wyodak coal liquefaction conversion under pseudocritical THQ-water/CO/H,S mixtures

Conversion”, %

Pressure (Psi) Temperature (“C)

H&/coal (g/g)

THQ/coal (gmol/g) H&CO (gmol/gmol) I

II

A. Effect of temperature at 30 minutes reaction time

3400

380

1.15

3550

400 1.09

3680

425 1.11

B.

Effect of time at 425°C reaction temperature

time (min)

0.01

219

86.5

94.5

0.01

219

92.5

95.8

0.01

219

95.5

96.8

3100

15

1.16

3680

30 1.00

3540

60 1.11

C.

Effect of H,S at 400°C reaction temperature

3620

30 1.13

3520

30 1.16

3550

30 1.09

D. Effect offeed ratio at 380°C reaction temperature

2700

15

1.65

3400

30 1.15

0.01

219

93.0

95.2

0.01

219

95.5

96.8

0.01

219

94.8 95.7

0.01

90.8

95.5

0.01

119

92.3

95.5

0.01

219 92.5

95.8

0.0136

219

84.9

96.0

0.01

219

86.5

94.5

_.

“Conversion I = toluene solubles; conversion II =THF solubles

The contribution of the WGS reaction studies did not

become a factor in the interpretation of the coal

liquefaction results, because of the rather low conversion

observed with the water/CO systems without solvent.

However, the WGS kinetic studies presented have a

validity on their own in showing the high activity of the

CoMoS catalysts, a fact not reported in the literature.

Sulphidation of the CoMo catalyst prior to reaction

increased dramatically its activity indicating that a

sulphided form of MO and Co (such as MoS, and Co,S,)

was likely responsible for the catalytic activity’“. The

formation of this sulphided surface appears to be the

reason why H,S enhanced the activity of the CoMo and

iron catalysts. The decrease in the activity of the catalyst

by the presence of organic solvents appears to be due to

adsorption and reaction of the solvent on the catalyst

surface. Experiments using catalyst powder form, did not

show a significant effect of particle size, ruling out

diffusional limitations.

Coal liquefaction using super-critical water only in the

FUEL, 1986, Vol

65,

September 1231



Catalytic l iq uefaction of coal: L. A. Am estica and E. E.

Wol f

absence of any hydrogen donor species reached 25%

conversion. This indicates that solubility enhancement of

some of the coal derived hydrocarbons in the supercritical

phase occurs but its overall value is still low at the

temperatures and pressures used in this work. Such

solubility enhancement can be attributed to the alteration

of the water physical properties at supercritical

conditions, in particular to changes in the dielectric

constant and polarity of the solvent2’. The 11 y0

desulphurization attained when using supercritical water,

attests that such reactions are also contributing to the

overall conversion.

increase in conversion in the presence of the other

solvents, is mainly due to the hydrocracking activity of

the CoMoS catalyst25.

The effect of the iron salts

depended on the solvent, the type of salt, and their

dispersion on the coal matrix. In general the conversion

observed in the presence of these salts was equal or less

than the values obtained without them. The inhibition

effect could be due to the suppression of the H,S activity

due to sulphidation of the resulting iron phases without

sufficient generation of H-donor capacity.

Addition of CO to supercritical water improved coal

conversion to 33 % and coal desulphurization to 20%.

This improvement can be due to some in

situ

generation

of hydrogen or by direct reaction of CO with coal derived

molecules. The presence of hydrogen can stabilize the free

radicals produced during coal thermolysis thus increasing

the yield to toluene soluble products. Alternatively CO

can react directly with some of the coal derived

hydrocarbons thus increasing conversion. The reactions

of CO with thiol, alcohols and ethers have been reported

in the literature10,21.

Finally, conversion ofthe subbituminous Wyodak coal

to THF soluble products was almost complete, which is

expected due to the differences in coal rank. The effect of

the operating variables was similar to results obtained

with the Illinois coal, except that retrogressive reactions

were evident at reaction times longer than 30min.

ACKNOWLEDGEMENTS

The support of this work by a grant from the Electric

Power Research Institute (EPRI), is gratefully

acknowledged.

The effect of introducing H,S, which increased

conversion in most of the solvent/catalyst combinations

studied, is due to the combination of several factors.

Several authors have reported that H,S plays a role as a

hydrogen donor in the liquefaction of lignites and coal

model compounds”,“.

This could occur

oia in situ

H,

production by direct dissociation of H,S

via

sulphidation

of the iron minerals in the coal, or on the added

catalysts”. Alternatively, H,S can participate directly in

cracking and hydrogenation reactions as reported by Van

Buren22 and Abdel-Baset

et al ’

‘.

As pointed out previously, the most significant result

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Except for toluene, the solvent effects correlated with

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facilitate dispersion of the coal fragments. Several authors

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via

condensation reactions which

results in an increase in the nitrogen content of the high

boiling products

23*24

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Documents

Catalytic Liquefaction of Coal With Supercritical Water CO Solvent Media