Catalytic effects of NaOH and ZrO2 for partial oxidative gasification

of n-hexadecane and lignin in supercritical waterq

Masaru Watanabea, Hiroshi Inomataa,*, Mitsumasa Osadab, Takafumi Satoa, Tadafumi Adschiric,Kunio Araia,b

aResearch Center of Supercritical Fluid Technology, Tohoku University, 07 Aoba Aramaki,

Aoba-ku, Sendai 980-8579, JapanbDepartment of Chemical Engineering, Tohoku University, 07 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan

cInstitute of Multidisciplinary Research for Advanced Materials Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan

Received 18 April 2002; accepted 29 August 2002; available online 22 October 2002

Abstract

Partial oxidative gasification of n-hexadecane (n-C16) and organosolv-lignin (lignin) was studied by use of a batch type reactor in

supercritical water: 673 K, 0.52 cm23 of water density (40 MPa of water pressure at 673 K), and 0.3 of O/C ratio for the n-C16 experiments;

673 K, 0.35 cm23 of water density (30 MPa of water pressure at 673 K), and 1.0 of O/C ratio for the lignin experiments. The experiments

without O2 were also conducted for lignin (lignin decomposition). For all the cases (n-C16 partial oxidation, lignin decomposition, lignin partial

oxidation), NaOH or zirconia (ZrO2) was added in the system as catalysts. Through n-C16 studies, the catalytic effect of NaOH and ZrO2 on

partial oxidation in supercritical water were examined. In the case of lignin partial oxidation, we studied the possibility of partial oxidation in

supercritical water for gasification technique of wastes. The yield of H2 from n-C16 and lignin with zirconia was twice as same as that without

catalyst at the same condition. The H2 yield with NaOH was 4 times higher than that without catalyst. Thus, a base catalyst has a positive effect

on partial oxidation of n-C16 and lignin to produce H2. The catalytic effect of NaOH and ZrO2 was found to be enhancement of decomposition of

intermediate (aldehyde and ketone) into CO, through n-C16 studies. In the case of lignin studies, the enhancement of decomposition of the

carbonyl compounds by catalytic effect of NaOH and ZrO2 inhibit char formation and promotes CO and thus H2 formation.

q 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Gasification; Partial oxidation; Hydrocarbon; Lignin; Supercritical water; Sodium hydroxide; Zirconia

1. Introduction

In these days, an innovative, effective, and low cost

process for organic compound gasification to produce

hydrogen (H2) has been required significantly because fuel

cell, that is a new energy supplier, is almost ready to use in

near future. So far, an industrial gasification process has

been operated at higher than 1073 K. The high temperature

process requires a lot of energy and thus a decrease of

operating temperature has been desired for developing a low

cost process for energy production. Recently, some

researchers show that a low temperature gasification process

of biomass can be archived by use of supercritical water as a

reaction media and a reactant [13]. Kruse et al. [1], for

instance, show that alkali salt like potassium hydroxide

(KOH) and potassium carbonate (K2CO3) promote gasifica-

tion of a biomass model compound (pyrocatechol) in

supercritical water even at a low temperature (773 K). We

also reported that sodium hydroxide (NaOH) is an effective

catalyst for gasification of glucose and cellulose in low

temperature (673 K) of supercritical water [3]. In the report

[3], we reported that zirconia (ZrO2) was also effective for

H2 production from these biomass model compounds in

supercritical water.

On the other hand, hydrocarbon (a main component of

waste plastics) and lignin (a main component of wood

biomass consists of phenolic structure) is known to be

difficult to gasify even in supercritical water [46]. Adschiri

et al. [7], Arai et al. [8], and Watanabe et al. [9] reported that

partial oxidation of hydrocarbon (both a linear chain

0016-2361/03/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.

PII: S0 01 6 -2 36 1 (0 2) 00 3 20 -4

Fuel 82 (2003) 545552

www.fuelfirst.com

q Published first on the web via Fuelfirst.comhttp://www.FuelFirst.com

* Corresponding author. Tel.:81-22-217-7283; fax:81-22-217-7282.E-mail address: inomata@scf.che.tohoku.ac.jp (H. Inomata).

hydrocarbon and an aromatic hydrocarbon) in high density

(more than 0.25 g/cm3 of water density) and low tempera-

ture (673 K) supercritical water is favored to produce H2and CO selectively. However, the H2 yield from hydro-

carbon is still low (less than 2% of the hydrogen atom basis

of a raw material) [9]. Watanabe et al. [9] suggested that

partial oxidation of hydrocarbon in supercritical water

proceeds via formation of aldehyde and ketone (namely

carbonyl compounds). Kabyemela et al. [10] showed that

key compounds of glucose decomposition are also aldehyde

and ketone (such as glyceraldehyde, dihydroxyacetone, and

so on). As mentioned above, since NaOH and ZrO2 are

effective for the decomposition of glucose to produce H2[3], these catalysts are expected to be also effective catalysts

for partial oxidative gasification of hydrocarbons.

In this study, we performed partial oxidative gasification

of n-hexadecane (n-C16) and organosolv-lignin (lignin) in

supercritical water (673 K and 40 MPa for n-C16 or 673 and

30 MPa for lignin) with and without catalyst. The reason

why n-C16 and lignin are selected in this study is as follows:

(1) the decomposition n-C16 in supercritical water has been

studied by the authors [8,9] and thus we can consider the

catalytic effect of a catalyst in more detail, (2) lignin is a

main component wood biomass and well known to be a

compound that is difficult to decompose into gaseous

products [5,6]. Thus we consider that we can show the

possibility of partial oxidation for gasification of waste

treatment technique through the lignin studies. We focused

on the degree of gasification and H2 yield, and thus

quantitative analyses of liquid product of the reaction had

not been performed in the study. Firstly, we conducted

n-C16 experiments and compared with the previous data [9].

From the results of the n-C16 experiments, we discussed the

catalytic effect of NaOH and ZrO2 on partial oxidation in

supercritical water. Next, lignin decomposition in super-

critical water was also performed with and without catalyst.

Further, partial oxidation of lignin with NaOH and ZrO2was also conducted and then the effect of these catalysts on

partial oxidation of lignin in supercritical water was

examined. The mechanism of partial oxidation of lignin in

supercritical water and the effect of catalysts on it was

considered based on n-C16 partial oxidation. Finally, we

discussed the possibility of partial oxidation in supercritical

water for waste treatment technique.

2. Experimental

n-Hexadecane (n-C16: C16H34) was obtained from Wako

Chemical and organosolv-lignin (lignin) was purchased

from Aldrich and these compounds were used as received.

The molecular formula of lignin is C3.25H3.54O, which was

revealed by ultimate analysis. Sodium hydroxide (NaOH,

1 M aqueous solution) and used without further purification.

Distilled water was obtained from a water distillation

apparatus (Yamato Co., model WG-220). Zirconia (ZrO2)

catalyst was prepared by calcination of zirconium hydroxide

(Nakarai Tesque, Inc.) at 673 K for 3 h in air. The mean

value of surface area of ZrO2 catalyst was 110 m2/g from

BET analysis. The structure of zirconia observed by X-ray

was monoclinic and tetragonal mixture.

The reaction was carried out in a SUS 316 stainless

steel tube bomb reactor with an inner volume of 6 cm3

[8]. One can see the experimental procedure elsewhere

[8]. Briefly, the loaded amounts of samples (n-C16 and

lignin) were all 0.3 g. After loading of liquid and solid

samples, O2 gas was introduced from gas cylinder

through 1/16 line and a high-pressure stop valve. The

amount of loaded O2 was calculated by the loaded

pressure of O2 and the vacant volume of the reactor. In

the case of n-C16 experiments, the loaded amount of

water was 3.1 g (0.52 g/cm3) and the ratio of O (oxygen

atom of O2, not including O of H2O) to C (carbon atom

of the loaded organic compound) was 0.3 (O/C 0.3).From the literature [6], char formation was observed at

lignin decomposition in supercritical water, while a little

char formation at n-C16 decomposition [9]. Therefore,

required O2 for the lignin gasification must be higher

than that for n-C16 and O/C was set to be 1.0. Water

density was 0.35 g/cm3 for lignin experiments. For the

experiments using alkali, 0.1 mol/l of NaOH aqueous

solution was loaded instead of pure water. In the case of

the ZrO2 catalyst experiments, 0.3 g of a catalyst was

loaded. The reaction temperature was 673 K. The reac-

tion time of n-C16 experiments was always 5 min. Since

the catalytic effect of the catalysts on partial oxidation

was examined through the n-C16 experiments, the

experiments at the same reaction time were needed for

comparison [9]. For examining the decomposition

mechanism of lignin, the reaction time of lignin

experiments without O2 (lignin decomposition) ranged

from 15 to 60 min. The experiments at 15 min with O2,

that was the shortest residence time for lignin decompo-

sition without O2, was conducted because the possibility

of partial oxidation as a low temperature gasification

technique was discussed through lignin experiments.

The identification and quantification of produced gas

was conducted by GC-TCD (Shimadzu, model GC-7A,

and Hitachi, model GC163). For recovering liquid and

solid in the reactor, the reactor was washed with THF for

both n-C16 and lignin studies. Before washing of the

reactor with THF, an amount of water was added to

recover water soluble compound for lignin experiments.

THF insoluble (THFI, including char and/or the metal

oxide catalyst) was divided by filtration with membrane

filter. THF soluble (THFS) and water soluble was

roughly analyzed with GC-FID (Hewlett-Packard, model

6890) and GC-MS (JEOL, model Automass 20). The

amount of carbon (both inorganic and organic) in the

water solution was evaluated using TOC (total organic

carbon detector, Shimadzu, model TOC-5000A) for the

lignin studies.

M. Watanabe et al. / Fuel 82 (2003) 545552546

For n-C16 experiments, the product yield was evaluated

from carbon base and the H2 yield was evaluated from

hydrogen base of a loaded amount of n-C16 (C16H34):

yield mol% the recovered amountof carbon or hydrogen in aproduct

the loaded amount of carbon or hydrogen inn-C16H34100 1

For lignin experiments, the yield of gas and water-soluble

product containing C atom was evaluated from carbon base

and the H2 yield was evaluated from hydrogen base of a

loaded amount of lignin (C3.25H3.54O):

yield mol% the recovered amountof carbon or hydrogen in aproduct

the loaded amount of carbon orhydrogen inC3:25H3:54O100 2

The yield of THF insoluble was evaluated from weight base:

yield wt% the weight of THF insolublethe weight of loaded C3:25H3:54O

100 3

3. Results and discussion

3.1. Study of n-C16

3.1.1. Effect of ZrO2 and NaOH on partial oxidation

of n-C16 in supercritical water

First of all, we conducted partial oxidation of n-C16 with

and without NaOH and ZrO2 catalyst at 673 K, 0.52 g/cm3,

5 min, and 0.3 of O/C. For all the cases of n-C16experiments, (1) the main products were H2, CO, CO2,

C1C15 n-alkanes, C2C15 1-alkenes, some oxygenated

organic compounds (alcohol, aldehyde, carboxylic acid, and

ketone; in particular, aldehyde and ketone were the main

oxygenated organic products); (2) conversion of O2 was

always more than 90%; (3) conversion of n-C16 was always

around 15%, as same as reported previously [9]. Thus, the

catalyst addition does not increase the conversion of n-C16.

In this work, since we focus on H2 formation from

hydrocarbon, the gas product was firstly discussed.

Figs. 1 and 2 shows carbon compound yield and H2 yield

in the gas products, respectively. As shown in Fig. 1, CO

yield with the catalysts was higher than that without catalyst.

The order of CO yield is as follows: NaOH . ZrO2 .without catalyst. This order was the same as the order of H2yield, as shown in Fig. 2. This means that H2 formation was

closely related to CO formation. Fig. 3 shows the ratio of H2yield to CO2 yield (H2/CO2 ratio). When H2 is formed only

from water gas shift reaction (CO H2O $ CO2 H2),the H2/CO2 ratio must be unity. Although the H2/CO2 ratio

without catalyst was 0.3, those with ZrO2 and NaOH were

0.75 and 1.76, respectively. Ross et al. [11] and Elliott et al.

[12] suggested that the water gas shift reaction must be

promoted by alkali (such as NaOH) in sub- and supercritical

water. At the short residence time for the n-C16 experiments,

CO conversion into CO2 was not so high probably. As

suggested before [3,13], ZrO2 can work as base catalyst

even in supercritical water since the H2/CO2 ratio was

almost unity. Furthermore, the increase of H2/CO2 ratio with

the catalyst suggests that ZrO2 and NaOH inhibited the

direct oxidation into CO2 because CO2 formation was

possibly only from water gas shift reaction. One of the

reasons why the H2/CO2 ratio with NaOH was close to 2

were possibly incompleteness of CO2 recovery because CO2is well known to dissolve into alkaline (such as NaOH)

solution. We analyzed the amount of dissolved CO2 by use

of TOC at the lignin studies as described below, but we did

not analyze dissolved CO2 in the n-C16 studies. As

mentioned below in the lignin studies, there might be a

possibility of another pathway of H2 formation besides

water gas shift reaction, for example, the contribution of

thermal decomposition of hydrocarbons. At this time, we

consider that the above results indicates that these base

catalysts (ZrO2 and NaOH) promote partial oxidation into

Fig. 1. Gas products (carbon compound) yield of n-C16 partial oxidation in

supercritical water with and without catalyst.

Fig. 2. H2 yield of n-C16 partial oxidation in supercritical water with and

without catalyst.

M. Watanabe et al. / Fuel 82 (2003) 545552 547

CO, water gas shift reaction, and decompose some organic

compounds into CO and H2.

Fig. 4 shows the ratio of n-alkane to 1-alkene (n-alkane/1-

alkene ratio) in the THF soluble. The n-alkane/1-alkene ratio

with ZrO2 was slightly lower than that without catalyst. The

n-alkane/1-alkene ratio with NaOH was much lower than that

with ZrO2 and without catalyst. Thus the CO and H2formations were considered to relate to the n-alkane/1-alkene

ratio. As shown in our previous studies [4,9], the n-alkane/1-

alkene ratio implies the ratio of the rate of unimolecular

reaction (decomposition) to that of bimolecular reaction

(hydrogen abstraction), based on pyrolysis mechanism [14,

15]. According to this idea, the rate of decomposition was

enhanced by adding base catalyst (ZrO2 and NaOH). Buhler

et al. [16] suggest that CO was formed via HCHO

decomposition with OH radical at glycerol decomposition

in supercritical water and that the formation of HCHO from

some intermediates (an aldehyde) was enhanced by OH ion

in supercritical water. As reported on gas phase pyrolysis [17,

19,20], a ketone was also a precursor of CO. According to

these suggestions, decomposition of an aldehyde and a

ketone into CO was enhanced by adding OH ion (namely

base catalyst such as ZrO2 and NaOH). Since n-alkane/

1-alkene ratio decreased by adding base catalyst as shown in

Fig. 4, a by-product of decomposition of an aldehyde and a

ketone was assumed to be 1-alkenes.

Thus, though the n-C16 studies, we suggest the pathways

of partial oxidation and the effects of ZrO2 and NaOH on

n-C16 partial oxidation as follows.

Partial oxidation into intermediates:

hydrocarbon!O2 aldehyde ketone others R-1HCHO formation from intermediate:

aldehyde andketone!base

HCHOothers probably1-alkeneR-2

HCHO decomposition into CO:

HCHO !OH radicalbase

CO R-3

Water gas shift reaction:

COH2O!base

CO2H2 R-4

3.2. Study of lignin

3.2.1. Effect of ZrO2 and NaOH on lignin decomposition

in supercritical water

The overall reaction of lignin including gas products in

supercritical water (at around critical point of water) has not

been reported so far. In order to clarify the effect of partial

oxidation on lignin reaction and the effect of catalyst on

partial oxidation, we first performed the lignin decompo-

sition in supercritical water. The experiments for lignin

decomposition were conducted with and without ZrO2 and

NaOH at 673 K, 0.35 g/cm3 of water density, and

1560 min. The products were categorized into gas, water

soluble, THF soluble, and THF insoluble products. The gas

products include H2, CO, CO2, and C1C4 alkane and

alkene. The water soluble include CO2 and some phenolic

compounds (catechol, guaiacum, and so on). In the THF

soluble products, there were some aromatic compounds

(toluene, propyl benzene, and so on) in addition of phenolic

compounds. All the yields of identified phenolic and

aromatic compounds were very low (less than 1 mol%).

Figs. 57 show the product distribution without catalyst,

with ZrO2, and with NaOH, respectively. Except for THF

insoluble, the yield of each compound was evaluated by

mole base to a loaded amount of lignin. The yield of THF

insoluble was evaluated by weight base. The water soluble

was from TOC value. At this moment, we did not evaluate

the amount of the yield of THF soluble. As shown inFig. 4. Ratio of n-alkane/1-alkene of n-C16 partial oxidation in supercritical

water with and without catalyst.

Fig. 3. H2/CO2 ratio of n-C16 partial oxidation in supercritical water with

and without catalyst.

M. Watanabe et al. / Fuel 82 (2003) 545552548

Figs. 57, although the water-soluble yields were almost

same 2025 mol%, the THF insoluble yield with catalyst

(4 13 wt%) was higher than that without catalyst

(18 wt%). Lundquist and Ericsson [18] observed HCHO

and phenolic compounds formation at lignin degradation

(Eq. (R-5)).

HCHO formation:

Lignin! HCHO phenolic compounds others R-5It is well known that phenolic compound can react with

HCHO to form phenolic resin (polymerization) [19].

Polymerization:

HCHO phenolic compound! resins R-6Thus we consider that the formation of HCHO Eq. (R-5)

was probably enhanced by base catalyst, as a result, the

yield of THF insoluble with base catalyst was higher than

that without catalyst. Next, H2 formation from lignin will be

discussed.

As shown in Fig. 5, the yield of H2 and CO2 slightly

increased with increasing reaction time, on the other hand,

the yield of CO has a maximum (1.26 mol% at 15 min,

1.41 mol% at 30 min, and 1.14 mol% at 60 min). This

indicates that water gas shift reaction proceeds gradually

even without catalyst. With ZrO2 (Fig. 6), the yield of H2and CO2 increased with increasing reaction time as well as

without catalyst. The yields of H2 with ZrO2 (4.0 mol% at

60 min) were almost twice as much as that without catalyst

(2.3 mol% at 60 min). The yield of CO with ZrO2 linearly

decreased with increasing reaction time. Comparing with

the time profile of CO and CO2 yield without catalyst, the

rate of water gas shift reaction was enhanced by adding

ZrO2. By adding NaOH (Fig. 7), the formation of H2 and

CO2 was significantly enhanced. The yield of H2 and CO2(15 and 9.3 mol% at 60 min, respectively) was quite higher

than that without catalyst (2.3 and 4.7 mol% at 60 min,

respectively). The CO yield with NaOH was remarkably

low at all the reaction time. This means that the rate of water

gas shift reaction was remarkably promoted by alkali. At

60 min of reaction time, the yield of CO2 was also enhanced

by adding ZrO2 (6.3 mol%, Fig. 6) and NaOH (9.3 mol%,

Fig. 7) compared to without catalyst (4.7 mol%, Fig. 5).

This indicates that the yield of CO which is the precursor of

CO2 was also enhanced by base catalyst (ZrO2 and NaOH).

This is possibly due to enhancement of the decomposition

rate of aldehyde and ketone, which are assumed to be

intermediates of lignin decomposition as well as n-C16partial oxydation, to form HCHO by base catalyst Eq. (R-2).

In addition, HCHO thermally decomposes into H2 and CO

at a low HCHO concentration (less than 0.1 mol/L at 673 K)

in the absence of O2 in supercritical water [20]:

HCHO thermal decomposition:

HCHO!CO H2 R-7

Fig. 8 shows the time profile of the H2/CO2 ratio with andFig. 6. Product distribution of lignin decomposition in supercritical water

with ZrO2 catalyst.

Fig. 5. Product distribution of lignin decomposition in supercritical water

without catalyst.Fig. 7. Product distribution of lignin decomposition in supercritical water

with NaOH catalyst.

M. Watanabe et al. / Fuel 82 (2003) 545552 549

without catalyst. The ratio was enhanced by adding ZrO2and NaOH. In the case of NaOH, the H2/CO2 ratio was 1.6 at

60 min. This means that there is another pathway of H2formation besides water gas shift reaction as mentioned

above (at the results of n-C16 studies, for example Eq. (R-7)).

3.2.2. Effect of ZrO2 and NaOH on lignin partial oxidation

in supercritical water

Through the above lignin decomposition studies

without O2, the formation of HCHO (Eq. (R-5)) must

be enhanced by adding base catalyst, as a result,

formation of CO (Eq. (R-3) or (R-7)) and THF insoluble

(Eq. (R-6)) was also enhanced. For promotion of

gasification and H2 formation, HCHO must be decom-

posed more effectively before polymerization with

phenolic compound to form THF insoluble. Buhler et al.

[16] suggested that HCHO decomposition into CO was

enhanced by OH radical (Eq. (R-3)). Thus, partial

oxidation of lignin with and without catalyst was

performed to examine the effect of partial oxidation on

promotion of gasification and H2 formation from lignin at

673 K, 0.35 g/cm3 of water density, 1.0 of O/C, and

15 min.

The main products were almost the same as without O2experiments. In this case, we also categorize the products

into gas, water soluble, THF soluble, and THF insoluble

products. As same as the case without O2, the yield of THF

soluble was not evaluated at this moment.

Fig. 9 shows the product distribution of carbon

compound. The yield of THF insoluble was calculated

by weight base and the others were by mole base, as well

as Figs. 57. For comparison, the results without O2 were

also shown in this figure. Without O2, the highest

gasification yield (CO and CO2 yield with NaOH) was

7 mol% at 15 min. In the case of partial oxidation,

gasification (CO and CO2 yield) was achieved more than

40 mol% regardless of the presence or absence of catalyst.

While the THF insoluble yield without catalyst was

enhanced by adding O2 (1.2 ! 6.0 wt%), that withcatalyst was inhibited by partial oxidation

Fig. 8. H2/CO2 ratio of lignin decomposition in supercritical water with and

without catalyst.

Fig. 9. Product distribution of lignin thermal decomposition and partial oxidation in supercritical water with and without catalyst.

M. Watanabe et al. / Fuel 82 (2003) 545552550

(3.6 ! 3.2 wt% with ZrO2 and 10 ! 3.3 wt% withNaOH). The water soluble decreased by partial oxidation

with and without catalyst. These phenomena indicate that

HCHO formation from lignin (Eq. (R-8)) proceeds by O2

as well as n-C16 partial oxidation (Eqs. (R-1) and (R-2))

and HCHO decomposition was enhanced by partial

oxidation as shown in Eq. (R-3).

Fig. 10. H2 yield of lignin thermal decomposition and partial oxidation in supercritical water with and without catalyst.

Fig. 11. H2/CO2 ratio of lignin thermal decomposition and partial oxidation in supercritical water with and without catalyst.

M. Watanabe et al. / Fuel 82 (2003) 545552 551

HCHO formation through partial oxidation:

lignin!O2 HCHO others R-8Fig. 10 shows the H2 yield with and without O2. By adding

O2, H2 formation was enhanced at all the cases, as shown in

Fig. 10. With ZrO2, the H2 yield (3.5 mol%) was twice as

much as that without catalyst (1.8 mol%). As well as the

case of n-C16 partial oxidation and lignin decomposition, the

H2 yield with NaOH (9.2 mol%) was 4 times higher than

that without catalyst (1.8 mol%). Fig. 11 shows the H2/CO2ratio. Although H2 yield was enhanced with O2 (Fig. 10), the

H2/CO2 ratio was inhibited at all the cases (Fig. 11). This

means that CO2 formed not only water gas shift reaction but

also direct oxidation. The another reason of low H2/CO2ratio was probably due to H2 combustion with excess O2because the partial oxidation was carried out at 1.0 of O/C.

In the case of 0.3 of O/C at n-C16 partial oxidation, H2/CO2ratio with catalyst was almost or more than unity as

described above. Thus, there is possibility that we can get

much H2 yield and H2/CO2 ratio by changing O/C value.

Through this study, it was found that partial oxidation with

base catalyst in supercritical water can be applied for H2formation from hydrocarbon (plastics) and lignin (biomass),

by due to enhancement of HCHO formation (Eqs. (R-2) and

(R-5)), HCHO decomposition (Eqs. (R-3) and (R-7)), and

water gas shift reaction Eq. (R-4).

4. Conclusion

Partial oxidation of n-hexadecane and organosolv-lignin

was studied by use of a batch type reactor in supercritical

water. The n-hexadecane experiments were carried out at

673 K, 0.52 cm23 of water density (40 MPa of water

pressure at 673 K), and 0.3 of O/C ratio, to examine the

effect of base catalyst (ZrO2 and NaOH). As the result, the

addition of catalyst did not increase the conversion of n-C16and promoted the formation of 1-alkenes and H2. Since the

H2/CO2 ratio was almost or more than unity, partial

oxidation into CO and water gas shift reaction was possibly

enhanced by base catalyst.

The lignin experiments were performed at 673 K,

0.35 cm23 of water density (30 MPa of water pressure at

673 K), 1.0 of O/C. The experiments without O2 were also

conducted for lignin. The yield of H2 from lignin with

zirconia was twice as same as that without catalyst at the

same condition for both with and without O2. The H2 yield

with sodium hydroxide (NaOH) was almost 4 times higher

than that without catalyst (with and without O2). Thus, a

base catalyst has a positive effect on decomposition and

partial oxidation of lignin to gaseous product such as H2.

Acknowledgements

The authors thank for the Grant-in-Aid for Scientific

Research (13750707) of the Ministry of Education and

Culture of Japan.

References

[1] Kruse A, Meier D, Rimbrecht P, Schacht M. Ind Engng Chem Res

2000;39:4842.

[2] Minowa T, Ogi T. Catal Today 1998;45:411.

[3] Watanabe M, Inomata H, Arai K. Biomass Bioenergy 2002;22:405.

[4] Watanabe M, Hirakoso H, Sawamoto S, Adschiri T, Arai K.

J Supercrit Fluids 1998;13:247.

[5] Funazukuri T, Wakao N, Smith JM. Fuel 1990;69:349.

[6] Yokoyama C, Nishi N, Nakajima A, Seino K. Sekiyu Gakkaishi 1998;

41:243.

[7] Adschiri T, Shibata R, Sato T, Watanabe M, Arai K. Ind Engng Chem

Res 1998;37:2634.

[8] Arai K, Adschiri T, Watanabe M. Ind Engng Chem Res 2000;39:4697.

[9] Watanabe M, Mochiduki M, Sawamoto S, Adschiri T, Arai K.

J Supercrit Fluids 2001;20:257.

[10] Kabyemela BM, Adschiri T, Malaluan RM, Arai K. Ind Engng Chem

Res 1999;38:2888.

[11] Ross DS, Blessing JE, Nguyen QC, Hum GP. Fuel 1984;63:1206.

[12] Elliott DC, Hallen RT, Sealock Jr. JL. Ind Engng Chem Prod Res Dev

1983;22:431.

[13] Watanabe M, Inomata H, Smith Jr. RL, Arai K. Appl Catal A Gen

2001;219:149.

[14] Watanabe M, Tsukagoshi M, Hirakoso H, Adschiri T, Arai K. AIChE

J 2000;46:843.

[15] Watanabe M, Adschiri T, Arai K. Ind Engng Chem Res 2001;40:2027.

[16] Buhler W, Dinjus E, Ederer HJ, Kruse A, Mas C. J Supercrit Fluids

2002;22:37.

[17] Berces T. The decomposition of aldehydes and ketones. In: Bamford

CH, Tipper CF, editors. Comprehensive chemical kinetics, vol. 5.

Amsterdam: Elsevier; 1972.

[18] Lundquist K, Ericsson L. Acta Chem Scand 1970;24:3681.

[19] Billmeyer Jr.FW. Textbook of polymer science, 3rd ed. New York:

Wiley; 1984.

[20] Watanabe M, Osada M, Inomata H, Arai K, Kruse A. Submitted to

Appl Catal A Gen..

M. Watanabe et al. / Fuel 82 (2003) 545552552

Catalytic effects of NaOH and ZrO2 for partial oxidative gasification of n-hexadecane and lignin in supercritical waterIntroductionExperimentalResults and discussionStudy of n-C16Study of lignin

ConclusionAcknowledgementsReferences