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Catalysis of SO24 =ZrO2 solid acid for the liquefaction of coal

Zhicai Wang a,*, Hengfu Shui a, Yanni Zhu a, Jinsheng Gao b

a School of Chemistry and Chemical Engineering, Anhui Key laboratory of Clean Coal Conversion & Utilization, Anhui University of Technology, 243002 Maanshan, Chinab College of Resource and Environmental Engineering, East China University of Science and Technology, 200273 Shanghai, China

a r t i c l e i n f o

Article history:

Received 9 May 2008

Received in revised form 29 October 2008Accepted 30 October 2008

Available online 18 November 2008

Keywords:

SO24 =ZrO2 solid acid

Hydro-liquefaction

Coal

Model compound

Catalysis

a b s t r a c t

In order to study the catalysis of SO24 =ZrO2 solid acid for the liquefaction of coal, a series of SO24 =ZrO2

solid acids were synthesized by the method of precipitationimpregnation. The catalytic behaviours of

the SO24 =ZrO2 solid acids for the hydro-liquefaction of Shenhua coal and model compounds, such as

diphenylmethane, bibenzyl and phenyl ethyl ether, were investigated. In addition, non-catalytic liquefac-

tion and the catalytic liquefaction under N2 were further compared with the catalytic liquefaction under

H2 in order to understand the catalytic mechanism of SO24 =ZrO2 solid acid. The results indicate that

hydro-liquefaction conversions of coal and model compounds are related to the strength, amount and

nature of acid sites on the surface of SO24 =ZrO2, and the strong acid site responds to their catalytic activ-

ities. The SO2

4 =ZrO2 solid acid catalyzes mainly the hydro-cracking, ring-opening and hydrogenation

reactions of coal to produce oil and gas during the coal liquefaction. The hydro-cracking reactions in

the liquefaction of model compounds and coal catalyzed by SO 2

4 =ZrO2 involved via carbenium ion inter-

mediate instead of traditional radicals intermediate.

2008 Elsevier Ltd. All rights reserved.

1. Introduction

As a viable option of the production of transportation fuels, the

direct liquefaction of coal is an issue of the higher efficiency and

cleaner utilization of coal in China. For direct liquefaction of coal,

catalyst plays an important role and attracts extensive attention.

However, most of researchers only concerned on the hydrogena-

tion activity of catalyst, in order to stabilize the fragments formed

during coal pyrolysis and remove the heteroatoms of liquefied

products. Fe, Mo and Ni based catalysts are usually used [17]. Tra-

ditional coal liquefaction processes require high temperature

above 400 C because the fragment of coal is produced by thermal

cleavage [8,9]. Therefore, a novel coal liquefaction catalyst to be

used under moderate conditions is very attractive in order to re-

duce the cost of operation [10,11].

Liquid acids such as CF3SO3H [11,12], HF + BF3 [13,14] and mol-

ten salt [1517], have been widely studied in a moderate liquefac-

tion of coal at temperatures ranging from 100 C to350 C with low

hydrogen pressure. However, these liquid acids are difficult to be

recovered and regenerated, and their corrosive nature and instabil-

ity may exclude their practical application [18]. Recently,

SO24 =MxOy solid acids with strong acidity and less corrosive are

found to be good catalyst for the synthetic reactions such as ester-

ification, etherification and alkylation, and the cracking reaction

[19]. In addition, the synergistic action between acid site and base

site on the surface of Mx

Oy

may catalyze the hydrogenation reac-

tion by ion mechanism [2022]. Therefore, it is worthy to be used

as a novel catalyst for the hydro-liquefaction of coal.

Since Tanabe et al. [23] discovered that SO24 promoted the cat-

alytic ability of Fe2O3 for direct liquefaction of coal in 1982, Kota-

nigawa and Yokoyama et al. [2427] had also studied the catalytic

behaviour of sulfated Fe2O3 catalysts. For example, Kotanigawa

et al. [27] speculated that Fe2O3 (SO24 ) might be a active form of

conventional FeS2 catalyst, and H2 adsorbed on the surface of

Fe2O3 (SO24 ) may be decomposed into H

+ and H by heterolysis.

But they only studied the transformation of sulfur and the effect

of acid properties of catalyst on its catalytic cracking ability. The

distribution of the products was not discussed. Although Pradhan

et al. [28] considered Fe2O3 (SO24 ) as a super acid, and speculated

that the super acidity of the catalyst catalyzed coal liquefaction to

some extent, they attributed such enhance to the suppress of the

agglomeration of metal oxide and the dispersity of catalyst.

Matsuhashi et al. [29] studied the catalysis of metal oxide pro-

moted by SO24 for the cracking of model compounds, but relation-

ship of the catalytic properties of catalysts with their acid

properties was not found. In China, Zhu [30] prepared a highly dis-

persed SO24 =Fe2O3 solid acid from NH4Fe(SO4)2, and studied the ef-

fects of acid properties of SO24 =Fe2O3 on coal liquefaction with

sulfur as promoter. Bronsted acid site of catalyst was found to be

the active sites for coal liquefaction, which can catalyze the hy-

dro-cracking of asphaltene to oil. Because Fe2O3 will be trans-

formed into sulfide iron under 300 C while sulfur is used as

promoter [18], the acid properties of SO24 =Fe2O3 surface changed

0016-2361/$ - see front matter 2008 Elsevier Ltd. All rights reserved.doi:10.1016/j.fuel.2008.10.040

* Corresponding author. Tel.: +86 13955530691; fax: +86 555 2311822.

E-mail address: zhicaiw@ahut.edu.cn (Z. Wang).

Fuel 88 (2009) 885889

Contents lists available at ScienceDirect

Fuel

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u e l

mailto:zhicaiw@ahut.edu.cnhttp://www.sciencedirect.com/science/journal/00162361http://www.elsevier.com/locate/fuelhttp://www.elsevier.com/locate/fuelhttp://www.sciencedirect.com/science/journal/00162361mailto:zhicaiw@ahut.edu.cn

8/4/2019 Catalysis of SO2

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during coal liquefaction. Therefore, it is disadvantage to study the

catalytic mechanism of SO24 =Fe2O3 with sulfur as promoter for

coal liquefaction.

In order to avoid the catalysis of FeS1x, which maybe generated

from SO24 =Fe2O3, and to study the catalysis of SO

24 =MxOy solid

acids for the liquefaction of coal, sulfated ZrO2 solid acids had been

used to catalyze the liquefaction of Shenhua coal in our previous

work [31]. The results showed that the conversion of coal catalyzed

by solid acid was higher than that by FeS or FeS + S. In this paper,

the acid property of the sulfated ZrO2 was characterized and its

catalytic mechanism was probed by direct liquefactions of coal

and model compounds.

2. Experimental

2.1. Coal and solvent

Shenhua coal (Chinese subbituminous coal) used in this study

was provided by 973 Program (National Basic Research Program

of China) research group. It was ground to less than 200 mesh,

stored under nitrogen atmosphere and used by drying under vac-

uum at 353 K overnight. The ultimate and proximate analyses of

coal are shown in Table 1. All solvents were used without further

purification.

2.2. Preparation ofSO24 =ZrO2

The hydroxide of Zr was obtained by hydrolization of ZrOCl2with aqueous ammonia at room temperature, and then the precip-

itated solution was filtered, washed and dried. The hydroxide of Zr

was further impregnated with aqueous sulfuric acid, dried and cal-

cined at specified temperature and time. A detailed description can

be found elsewhere [31]. All chemicals used as above were of re-

agent grade.

2.3. Liquefaction procedure of coal and model compounds

The liquefaction experiments were carried out in a 30 mL tub-

ing reactor shaken vertically. Dried coal (2.0 g) and catalyst

(0.5 g) were charged into the reactor together with 5 mL of tetralin

(THN) solvent. Before liquefaction, the reactor was purged with H2for several times and pressurized to the desired initial pressure of

5.0 MPa with H2. The reactor was submerged into an eutectic salt

bath, which had been heated to a temperature of 405 C in order

to keep the reactor to the desired working temperature (400 C)

in 10 min with agitating vertically at 120 times/min, and main-

tained at the temperature for 30 min. Then the reactor was

quenched to ambient temperature in a water bath, and the over-

head pressure in the reactor was released slowly.

The liquid and solid products of coal liquefactionwere recovered

fromthe autoclave by washing out and Soxlet extraction withtetra-hydrofuran (THF) [32]. The overall conversion was calculated from

the amount of THF-insoluble material (THFI). After THF was re-

moved by evaporation, the THF-solubles were extracted with hex-

ane to separate into hexane-insoluble (HI) and hexane-soluble

(HS) fractions. The HI was further fractionated into toluene soluble

(HITS)and toluene-insoluble (TITHFS) by extractionwith toluene.

The HITS and TITHFS were defined as asphaltene and preasphal-

tene, respectively. The conversion and the yield of asphaltene and

preasphaltene were, respectively, calculated on dry and ash-free

(daf) basis coal. The combined oil-plus-gas yield was obtained by

the difference, i.e. Gas + oil = conversion-AS-PA. Most of the runs

were made in duplicate andthe reproducibilitywas better than2%.

The liquefaction procedure of model compounds was the same

as that of coal. In the runs, 10% model compounds in THN solutions

were substituted into coal and solvent. The liquefied products of

model compound were characterized by GC/MS and quantified

by GC with standard curve method.

2.4. Characterization of liquefaction derivatives

The IR spectra of liquefaction residue (THFI), AS and PA coming

from liquefaction of coal were measured by PE-Spectrum One IR

spectrometer. The solid-state product was mixed with KBr and

the mixture was pressed into a pellet. The liquid product was

determined by film coating method. The spectra were recorded

at room temperature.1H-NMR spectra of AS and PA, which were dissolved in d5-pyr-

idine solvent, were obtained using Brucker AM500 (500 MHz). The

element analysis was carried out in Elementar Vario EL III.

3. Results and discussion

3.1. Hydro-liquefaction of coal catalyzed by SO24 =ZrO2 solid acids

The distributions of acid sites of the SO24 =ZrO2 solid acids pre-

pared at different calcination conditions are quite different; there-

fore, the catalytic properties of the solid acids are varied. In order

to explore the catalysis of SO24 =ZrO2 solid acids for coal liquefac-

tion, the SO24 =ZrO2 solid acids calcined at different conditions

were used. Table 2 shows the conversions and the liquefied prod-

uct distributions of Shenhua coal catalyzed by SO24 =ZrO2.

From Table 2, it can be found that the conversion of Shenhua

coal liquefaction increases with the increase of calcination temper-

ature of SO24 =ZrO2 up to 650 C, at which the conversion reaches

76.8%, and then the conversion decreases with the increased calci-

nation temperature. According to our recent work [33], there are

two types of acid sites on the surface of SO24 =ZrO2 solid acid.

The SO24 =ZrO2 calcinated above 550 C shows most of Lewis acid

site. The intensity of acid site and the percent of strong acid site

of SO24 =ZrO2 increase with the increased calcination temperature.

The SO24 =ZrO2 calcinated at 650 C shows not only a lot of stronger

acid sites but also higher density of acid site compared to the other

SO24 =ZrO2 calcinated at 450750 C. The result suggests that the

conversion of coal liquefaction is related to the strength, amount,

and nature of acid site of SO24 =ZrO2, and the Lewis acid site re-

sponds to the catalytic activity of SO24 =ZrO2 for coal liquefaction.

The more the amount of stronger acid sites, the higher the activity

of SO24 =ZrO2 and the conversion of coal liquefaction.Table 2 also shows that the effects of SO

24 =ZrO2 properties on

the distributions of liquefaction products are very complicated.

There are a lot of reactions during the coal liquefaction, such as

hydrogenation, decomposition, condensation, dealkylation and

Table 1

Ultimate and proximate analyses of Shenhua coal.

Sample Ultimate analysis (wt%, daf) Proximate analysis (wt%)

C H N S O* Ad Vdaf Mad

Shenhua coal 80.13 4.88 1.06 0.42 13.51 5.52 38.24 9.34

* By difference.

Table 2

Results of the liquefaction of coal catalyzed by SO24 =ZrO2 solid acid.

Preparation conditions of

catalyst

Conversion/

%

Distribution of products/%

Preasphaltene Asphaltene Oil + gas

500 C, 3 h 56.5 37.1 35.9 27.0

550 C, 3 h 59.2 28.5 39.7 31.8

600 C, 3 h 69.9 32.9 24.3 42.8

650 C, 3 h 76.8 36.1 30.5 33.4

700 C, 3 h 67.0 38.8 26.3 35.0

886 Z. Wang et al. / Fuel 88 (2009) 885889

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etc., dependent on the strength of acid sites. For example, the

strong acid site is favorable for catalyzing the decomposition and

isomerization of carbon skeleton, the medium strong acid site is

favorable for the dealkylation of alkyl aromatics. The hydrogena-

tion and hydrogen transfer reaction are catalyzed by the bifunc-

tional catalyst with acid and base sites together [34,35]. The

distribution of liquefaction products shows that the yield of Oil +

gas increases with the calcination temperature of SO2

4 =ZrO

2up

to 600 C, and the lowest value is obtained when the SO24 =ZrO2

was calcinated at 500 C. It suggests that weaker acid site formed

by calcination at lower temperature only catalyzes the breakage

of weak covalent bond such as ether and ester bonds to give higher

yields of PA and AS, and lower yield of Oil + gas. The increased

strength of acid sites of SO24 =ZrO2 is advantageous to improve

the catalytic activity for the dealkylation and fragmentation of

hydroaromatic ring resulting in the increase yields of Oil + gas,

PA and AS. However, the stronger acid site can also catalyze the

condensation of coal fragments to promote the regressive reac-

tions. When the SO24 =ZrO2 was calcinated at 650 C, the PA and

AS yields markedly increased, and the Oil + gas yield decreased

compared to that the liquefaction of coal catalyzed by the

SO24 =ZrO2 calcinated at 600 C. For the SO

24 =ZrO2 prepared at

700 C for 3 h, the total amount of acid site reduced sharply com-

pared to that of the other catalysts [33], and the decreased amount

of acid site results in the decrease of the conversion and the varia-

tion of the product distribution.

3.2. Characterization of liquefaction products catalyzed by SO24 =ZrO2solid acids

Figs. 1 and 2 show the IR spectra of PAs and liquefied residues

catalyzed by the SO24 =ZrO2 prepared under different conditions.

It can be observed from the IR spectra of PAs that the absorption

peak of OH (near to 3400 cm1) increases with the increasing cal-

cination temperature for catalyst except at 650 C for 3 h. However,

the absorption peak of OH in the liquefaction residues decreases

with the increase of the calcination temperature of the catalyst.It indicates that the OH content of the residue decreases and that

of PA increases with the increased calcination temperature for the

catalyst. Weaker acid site formed at lower calcination temperature

can only catalyze the breakage of weaker covalent bonds of coal to

product PA, so the residue contains more OH groups. With the in-

creased calcination temperature, the SO24 =ZrO2 shows higher ratio

of strong acid site to weaker acid site [33], and can catalyze the

pyrolysis of carbon skeleton of coal to PA, so the OH content ofPA increases simultaneously with the decreased content of OH

in the residue. The SO24 =ZrO2 calcinated at 650 C for 3 h, which

exhibits the highest acid strength and more strong acid site [33],

can catalyze the decomposition of coal and PA into lower molecu-

lar weight products, so the contents of OH in the residue and PA

are both low. Therefore, it can be speculated that the OH groups

in the residue and PA are mainly phenolic one, which is in accor-

dance with the existence of OH in Shenhua coal we found before

[36], besides a little of OH may come from the breakage of ether

and ester functional group. In addition, the relative absorption

peak of aromatic carbonyl (1650 cm1) to that of aromatic ring

(1610 cm1) in the IR spectra of PAs and liquefied residues cata-

lyzed by the SO24 =ZrO2 calcinated at 650 C and 700 C is weaker

than that calcinated at other temperatures. The absorption peakof aromatic carbonyl in the IR spectrum of liquefied residue cata-

lyzed by the SO24 =ZrO2 calcinated at 600 C almost disappears. In

our previous work, the absorption peaks of aromatic carbonyl in

PAs are stronger while FeS was used as catalyst [31]. It suggests

that strong acid site is also favorable for catalyzing the decomposi-

tion of carbonyl structure in coal and PA to give more Oil + gas.

Thus, the results of IR spectra characterization of liquefied prod-

ucts further support that the strong acid site is responsible for

the coal liquefaction by catalytic cracking reaction.

3.3. Effects of liquefaction atmosphere on the liquefaction of coal

catalyzed by SO24 =ZrO2 solid acids

In order to further explore the catalytic activities of theSO

24 =ZrO2, the liquefaction of coal catalyzed by SO

24 =ZrO2 under

different atmospheres were carried out. Fig. 3 shows the conver-

sions and distributions of the liquefaction products of Shenhua coal

under N2 and H2 catalyzed by the SO24 =ZrO2, which was prepared

at 650 C for 3 h, and the liquefaction under H2 without catalyst,

respectively. Compared to the non-catalytic liquefaction, the incre-

ment of liquefaction conversion is near to 16% when the SO24 =ZrO2

was used as catalyst. Meanwhile, the conversion under N2 is the

lowest but the Oil + gas yield is similar to that under H2, and the

lower yields of AS and PA are respond for the decreased conversion

under N2 compared to that under H2. It suggests that the

SO24 =ZrO2 shows obvious catalytic activity for coal liquefaction,

especially for the decomposition of coal to give higher yields of

the oil and gas. In addition, H2 also shows a promotion for the liq-

uefaction of coal resulting in distinct increase of PA yield.Fig. 1. FTIR spectra of preasphaltene catalyzed by SO24 =ZrO2 solid acid: ae

calcinated at 500 C, 550 C, 600 C, 650 C and 700 C, respectively.

Fig. 2. FTIR spectra of liquefied residues catalyzed by SO2

4 =ZrO2 solid acid: ae

calcinated at 500 C, 550 C, 600 C, 650 C and 700 C, respectively.

Z. Wang et al. / Fuel 88 (2009) 885889 887

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Tables 3 and 4 show the results of element analyses and struc-

tural parameters of liquefaction products, respectively, under dif-

ferent conditions. H/C ratio of liquefaction residue under H2 with

or without catalyst is similar to 0.62, but the H/C ratio of liquefac-

tion residue under N2 increases to 0.67. The transformation of coal

matrix to PA is mainly ascribed to the hydro-cracking, predomi-

nated by the capacity of hydrogen donation. The liquefaction under

N2 yields lower PA, and gives higher H/C ratio of the residue due to

lower capacity of hydrogen donation. However, the PA is easy to

contact with the catalyst and solvent (hydrogen donator) and be

catalyzed into AS or Oil + gas. So, the lower H/C ratio of the PA

and higher yield of the AS were obtained during the catalytic

liquefaction.

The aromaticity of the PA from the catalytic liquefaction is high-

er than that from the non-catalytic liquefaction, as shown in

Table 4. It suggests that the alkyl side chains in the PA were

removed by the catalytic decomposition. Meanwhile, the hydrogen

distribution shows that the percentage of Hc is the highest in the

AS coming from the non-catalytic liquefaction, and is the second

highest from the catalytic liquefaction under N2. It suggests that

these ASs contain some longer alkyl side chains due to the weaker

cracking during the non-catalytic liquefaction. Meanwhile, the

HAU/CA (condensation index of aromatic ring) of AS coming from

the catalytic liquefaction under H2 is distinctly higher than that

from the catalytic liquefaction under N2 and the non-catalytic liq-

uefaction under H2. It indicates that the ring-opening reaction oc-

curs during the transformation from PA and/or coal to AS when the

SO24 =ZrO2 and hydrogen gas are simultaneously used. Because the

intermediates of ring-opening reaction catalyzed by the SO24 =ZrO2

can be immediately stabilized by the hydrogenation. Meanwhile,

HAU/CA of PA coming from the catalytic liquefaction under H2 is

the lowest in comparison with those of other PAs. It further con-

firms that the PA in the liquefaction catalyzed by the SO24 =ZrO2

under H2 is mainly high condensation aromatic fragments with

lower reactivity.

In addition, the catalytic hydrogenation occurs obviously in the

process of AS formation so as to give the AS with higher H/C ratio in

the catalytic liquefaction under H2. The structural parameters of AS

also indicate that the catalytic hydrogenation is favorable for

decreasing the aromaticity of AS under H2. Therefore, the catalytic

activity for the ring-opening and hydro-cracking reaction is the

main catalysis of SO24 =ZrO2 in the liquefaction of coal and the

catalysis for the hydrogenation can also be observed, especially

for the hydrogenation of AS.

3.4. Hydro-liquefaction of model compounds

Based on the structure of coal, diphenylmethane (DPM), bibenzyl

(DPE) and ethoxylbenzene (PEE) were selected as model com-

pounds of coal. They were hydro-liquefied in THN solvent in orderto further probe the catalytic mechanism of SO

24 =ZrO2 for the

liquefaction of coal.

Table 5 shows that the conversions of all model compounds in-

crease with the increased calcination temperature of SO24 =ZrO2

from 500 C to 650 C, and the highest conversion is obtained at

650 C for all the model compounds. Further, the conversions of

all the model compounds decrease when the catalyst was calcined

at 700 C. Thus the effects of calcination temperature on catalytic

activity of SO24 =ZrO2 during the hydro-liquefaction of the model

compounds are in accordance with that of the liquefaction of coal.

The catalysis of SO24 =ZrO2 maybe attributed to the strong acid site

on the surface of SO24 =ZrO2. The stronger the acidity of acid site

and the more the strong acid site, the higher the catalytic activity

of SO24 =ZrO2 during the liquefaction of coal. It was found by the

GC/MS characterization that the liquefied products of model com-

pounds consist of the crackates by the rupture of the bridging bond

along with a few of hydrogenated products. Therefore, it also

Table 3

Results of element analysis of Shenhua coal liquefaction products.

Samples Liquefaction conditions Cdaf/% Hdaf/% H/C

Asphaltene H2 catal 83.0 6.6 0.95

N2 catal 82.2 6.3 0.92

H2 non-catal 80.6 6.2 0.92

Preasphaltene H2 catal 82.3 5.4 0.79

N2 catal 80.6 5.4 0.80

H2 non-catal 80.7 5.6 0.83

Residue H2 catal 62.0 3.2 0.62

N2 catal 64.1 3.6 0.67

H2 non-catal 68.5 3.6 0.63

Raw coal 79.6 4.8 0.72

Table 4

Results of 1H NMR analysis and structure parameters of Shenhua coal liquefaction

products.

Sample Liquef action

conditions

Hydrogen

distribution/%

Structure

parameters

HA Ha Hb Hc fa d HAU/CA

Asphaltene H2 catal 21.5 26.6 42.2 9.8 0.63 0.38 0.53

N2 catal 22.2 22.8 39.5 15.5 0.65 0.34 0.48

H2 non-catal 23.1 21.7 35.1 20.0 0.65 0.32 0.48

Preasphaltene H2 catal 22.0 33.6 24.2 5.4 0.75 0.43 0.41

N2 catal 30.4 29.0 21.1 6.1 0.77 0.32 0.47

H2 non-catal 21.0 32.4 29.9 5.7 0.72 0.44 0.43

Table 5

Hydro-liquefaction conversion of model compounds with SO24 =ZrO2 solid acid

prepared under different calcining temperature.

Preparation conditions of catalyst Conversion/%

DPM DPE PEE

500 C, 3 h 21.7 1.7 15.1

550 C, 3 h 26.3 2.1 17.2

600 C, 3 h 34.3 2.7 27.1

650 C, 3 h 53.9 4.3 40.6

700 C, 3 h 26.5 4.1 26.0

27.3

23.4

25.6

10.6

14.8

25.7

20.6

16.1

22.2

0

10

20

30

40

50

60

70

80

Yield/%

H2 N2 H2 without

catalyst

Oil+Gas

Asphaltene

Preasphaltene

Fig. 3. Distributions of liquefied products under N2, H2 and non-catalyst.

888 Z. Wang et al. / Fuel 88 (2009) 885889

8/4/2019 Catalysis of SO2

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proved that SO24 =ZrO2 shows not only better catalytic cracking

activity but also great catalytic hydrogenation activity during the

coal liquefaction.

Meanwhile, Table 5 also shows that the conversions of model

compounds catalyzed by SO24 =ZrO2 increase in turn DPE, PEE

and DPM. For example, conversions of DPE, PEE and DPM are

4.25%, 40.56% and 53.89%, respectively, when the catalyst is calci-

nated at 650 C for 3 h. During the liquefaction of coal and the hy-

dro-cracking of model compounds, it is generally thought that the

homolysis of linkage bond in coal or model compounds firstly gives

the free radical. Then it is stabilized by hydrogenation transforma-

tion or catalytic hydrogenation. Shimizu et al. [37] found that BPE

and DPM show higher reactivity in superacidic medium compared

to biphenyl ether, and thought that the cracking reaction of model

compounds catalyzed by acid followed the carbenium ion mecha-

nism due to higher stability of benzyl cation. According to the free

radical mechanism, the activity of DPE reaction should be higher

than that of DPM because the bond of CalkCalk of ethylene in

DPE is weaker than the bond of CalkCar in DPM. However, our re-

sults show that the conversion of DPM is much higher than that of

DPE. Therefore, it is suggested that the cracking reactions of model

compounds and coal catalyzed by SO24 =ZrO2 may take place via

carbenium ion intermediate instead of radical intermediate.

4. Conclusion

Catalyticproperties of SO24 =ZrO2 solid acids for coal liquefaction

are related to their acid strength, amount and nature of acid sites.

The strong acid site dominates their catalytic activities. Catalytic

activity of SO24 =ZrO2 and liquefaction conversion of coal increase

with increasingof theamount ofstrong acid sites.SO24 =ZrO2 mainly

catalyzes the hydro-cracking, ring-opening and the hydrogenation

to generate the oil and gas during the liquefaction of coal. Effects

of catalyst acidity on the liquefaction of the model compounds are

accordance with the liquefaction of the coal. The hydro-cracking

reaction of model compounds catalyzed by SO24 =ZrO2 is via carbe-

nium ion intermediate instead of radical intermediate.

Acknowledgements

This study was supported by the National Natural Science Foun-

dation of China (20776001, 20676001). The authors gratefully

acknowledge the 863 Program of China (2006AA05Z314,

2007AA06Z113) and the International Cooperative Project of Anhui

Province (07080703001). The authors also appreciated the finan-

cial support of innovative group of Anhui Province Coal Resource

Processing & Cleaning Utilization.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, in

the online version, at doi:10.1016/j.fuel.2008.10.040 .

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