リグノセルロース系バイオマスの水熱分解過程における金属溶出挙動

誌名誌名 日本食品工学会誌 = Japan journal of food engineering

ISSNISSN 13457942

著者著者

熊谷, 聡太田, 真由美中野, 寿美林, 信行坂木, 剛甲斐田, 泰彦

巻/号巻/号 9巻2号

掲載ページ掲載ページ p. 109-114

発行年月発行年月 2008年6月

農林水産省 農林水産技術会議事務局筑波産学連携支援センターTsukuba Business-Academia Cooperation Support Center, Agriculture, Forestry and Fisheries Research CouncilSecretariat

]apan ]ournaJ of Food Engineering， Vo1. 9， No. 2， pp. 109 -113， ]un. 2008

く〉く>く>Original Paper 0く>く〉

Elution Behavior of Metals during Hydrothermal Decomposition

of Lignocellulosic Biomass

Satoshi KUMAGAI1，a，t， Mayumi UTA¥ Sumi NAKANO¥ Nobuyuki HAYASHI2，

Tsuyoshi SAKAKI3 and Yasuhiko KAIDA3

l]unshin ]unior Collage， Department 01 Food and Nutrition， 1-1-1 Chikushigaoka， Minami-ku， Fukuoka 815-8510，] apan 2 Saga Universiか"Faculか01Agriculture， 1 Honjyo， Saga-古hi，Saga 840-8502， ]apan

3AlST， Biomass lechnology Research Center， 807-1 Shukz付加chi，Tosu， Saga 841-o052，]apan

This paper describes the elution behavior of metals during hydrothermal decomposition of rice hulls at 200

0

C using a percolation type reactor. Through that treatment， the rice hulls were converted to solubilized products at 45.9wt% yield. The solubilized products were mainly arabinose，

xylose， and xylooligosaccharides derived仕omhemicellulose. While， cellulose was not decomposed

in this treatment Results showed that the elution behavior of metals with hydrothermal treatment is cJassifiable into two patterns. First， alkali metals， phosphorus， boron， and aluminum elution did not depend upon the temperature， but rather on the treatment time. On the other hand， elution of heavy metals， alkaline earth metals， and arsenic depends upon temperature. That is to say， raising the purity of organic matter might be possible by lengthening the time of the 1st fraction and inducing full elution to obtain high-quality organic matter with few metals in the 4th and the 5th仕action.Key words: biomass， hydrothermal treatment， metals， hemicellulose， saccharification

1. Introduction

From viewpoints of global environmental problems and

diminishing fossil-fuel resources， renewable and carbon-

neutrallignocellulosic biomass has been drawing attention

as an environmentally friendly resource. For that reason，

we have been studying application of hydrothermal reac-

tions for utilization of lignocellulosic biomass [1-9].

Hydrothermal treatn'lent of lignocellulosic biomass has

been examined in many studies. Bobleter [10，111. a pio-

neer of this field， cJarified about the hydrothermolysis

mechanism using cellobiose as a model component of bio-

mass. Early studies revealed that hydrothermolysis was

not dependent on pH， at least in the range of pH 3-7.

τnen， Adchiri [12] and Sasaki [13， 14] et al. examined

hydrothermolysis of cellulose and glucose in supercritical

water (SCW). However， for such SCW reactions， the rapid

reaction rate made control of the reaction difficult.

For that reason， we started to study hydrothermolysis

of biomass in hot-compressed water (HCW)， which has a

lower pressure (-10 MPa) and temperature (-3000

C)

(Received 29 J an. 2∞8: ac四 pted13 May. 2∞8)

a. Present address: Saga university， faculty of agriculture

(1 Honjyo， Saga.母hi，Saga 84().8502. Japan)

F剖 092-552-2707，E-m出1:kumag副 s@ho加 ail.co.jp

than SCw. We have already reported about hydrothermal decom-

position behavior ot organic matter (cellulose [1，2，71. hemicellulose [4，5，9] and lignin [5，6]) in biomass.

Results of those studies demonstrated that components

of hemicellulose and cellulose are recoverable as fractions

of mainly various oligosaccharides by treating the biomass

with a stepwise increase of HCW temperature using a per-

colator type reactor [3，8]. Specifically， the separation

method comprises the following steps: removal of easily

soluble components such as tannin and free saccharides

through treatment at 130oC; separation via solubilization of

hemicellulose as a企action，mainly of oligosaccharides， by

treatment at 140-220oC; and separation via solubilization

of cellulose as a fraction， mainly of oligosaccharides， at a

temperature higher than 230oC. Obtained saccharides can

be used as functiona1 foods and feedstocks for fermentation.

We have already reported saccharification behavior of

rice hulls， which are a main agricultural residue in ]apan

[8]. Rice hulls have a high ash content varying from very

13.2-21.0% [15]. However， elution behavior of metals

from biomass has not been elucidated. Elution of metals

might engender various problems such as harm for

humans [16， 171. fermentation inhibition [18， 191. and

sca1e for equipment. Therefore， it is important to investi-

Satoshi KUMAGAI， Mayumi OTA， Sumi NAKANO， Nobuyuki HAYASHI， Tsuyoshi SAKA悶，Yasuhiko KAIDA

in the each effluent was removed by heated at 1050

C and

the solubilized products were obtained.τbe residue in the

reactor was dried at 1050

C. The products yield was ca1cu-

lated on the feed dry base as follows;

Solubilized products yield (w出)= (amount of solubi-

lized products/amount of feed dry sample) X 100

Residual yield (wt幼=(amount of residue/amount of

feed dry sample) X 100

A half of each effluent was treated with lN HCl solution

at 1000

C for 1 h; then， it was filtrated. Each fil仕atesample

was then analyzed for some metals of four groups (alkali

metals-K and Na; alkaline earths-Mg and Ca; heavy met-

als-Cd， Pb， Zn and Cu; semi-metals-As and B) using an

inductively coupled plasma atomic-emission spectrometer

(SPS 1200AR; Seiko Instruments Inc.， ]apan).

gate elution behavior of metals from biomass.

In this study， elution behavior of metals together with

organic matter from rice hulls was investigated at 2000

C

using a percolator type reactor. At 200oC， hemicellulose

was solubilized， whereas cellulose was not solubilized [5]

That is to say， it is possible to企actionatehemicellulose

and cellulose under this temperature condition. For that

reason， treatment at this temperature was adopted in this

study.

Experimental

2.1 Materials

Rice hulls from Saga prefecture Gapan) were used in

this experiment.τbe rice hulls were pulverized using a

mill (rotor speed mill P-4; Fritsch GmbH); they were

sieved before the experiment to obtain 24-60 mesh.

2.

110

Results and Discussion

3.1 Solubilization and saccharification behavior

Fig. 2 shows solubilization behavior of rice hulls. For 4

min after the start of flow at room temperature， generation

of solubilized products was hardly observed. During the

next 8 min， when the temperature of HCW reached about

200oC， the accumulated yield of solubilized products was

7.1w仇Afterthe temperature reached 200oC， the genera-

tion of solubilized products became markedly rapid.

During the subsequent 4 min， the cumulated yield was

33.3wt%. When processed for 20 min (including cooling

step: 4 min)， the accumulated yield reached 45.9wt%.

Overall mass balances were 45.9wt% for solubilized prod-

80

100 Q) 回国

4コ~ τコてコu Q) ‘+ー

雪"tJ

ま40てコQ) N

4ココO cn

20

250

200

。。150 ~

コ+' 伺.... む

100 E む

ト

50

-ー・ー.一ーーー・ -・ ー.、e . .

. . . . . . . .

. . . .

.

3.

2.2 Hydrothermal treatment

One gram of rice hull powder (24-60 mesh) was

charged in a percolator type reactor (10.2 mm i.d. X 46.7

mm length， 3.8 mL). Both ends of the reactor were capped

with sintered filters (average pore size: 5μm).百len，it

was connected with HCW flow type equipment. A sche-

matic diagram of the equipment is depicted in Fig. 1. The

equipment consists of a deionized-water tank， high-pres-

sure pump， heater， reactoにcooler，backpressure regulator，

and reservoir. Details of the operation method are identi-

cal to that explained in a previous paper [8].

τbe hydrothermal treatment experiment was carried

out for 32 min (including a room temperature step of 4

min， a temperature increase step of 6 min， and a cooling

step of 4 min) at 2000

C (3.0 MPa， 10 mL/min). Effluents

were collected at 4-min intervals. A pH of each effl血uent

f仕r問actionwas measured using a pH meter (βSR-12止;Horiba

Ltd.ふSaccharideconcentrations were analyzed using an

HPAE-PADのX一.-50∞Oα;Dio叩nexCor叩pβω.)川[4].百1児en凡， the water 60

e

uu pa

pav'

陀ぬ

p

a

L

K

U

「lil--

C

E

-

-

」

-

a

e

-

-

-

B

r

ト「lL

ζ

~

b

「

o

&'

FいM曹2M e

D円8O

(Fr. No.l Lーー一一」

28 32

守，

aay

i

。，‘

5 6

L一一一一」

16 20

Time (min)

4

12

qd

i

Q

U

ηζ

O

Reservoir

Cooler

Fig. 2 Solubilization behavior of rice hulls in the process of

hydrothermal treatment.ー+ー ;Solubilized products yield，

ーーー;Temp

Deionaized-water

Fig. 1 Schematic diagram of the HCW f10w type apparatus.

111

3.2 Elution behavior of metals

Elution behavior of metals during hydrothermal treat-

ment is c1assifiable into two patterns. Figure 6 shows the

time course of metal (p， A!， K， Na and B) concentration in

the process of hydrothermal treatment. These metals did

not depend upon the temperature， but rather on the treat-

ment time.

Elution Behavior of Metals during Hydrothermal Decomposition of Lignocellulosic Biomass

ucts and 53.8wt% for residues.

Fig. 3 shows the change in the solubilized products

yield and the pH of effluent in each fraction. The yield

tended to increase as the treatment temperature became

higher. At the 4th仕action，the highest yield (26.2w出)was

indicated. It subsequently decreased.

The pH was high during the first 8 min. Then it

decreased as the concentration of solubilized products Figure 7 shows the time course of metal (Cd， Cu， Pb，

Zn， As， Ca and Mg) concentration in the process of hydro-

therma1 treatment of rice hulls. First， for heavy metals，

alkaline earth metals and arsenic depend upon the tem-

perature.ln the 1st fraction， metals adsorbed on the sur-

face and contaminated from soil might be eluted.

However， the amount of elution was very small. Then， in

4th fraction， when the temperature reached 2000

C， great

amounts of metals were eluted again. This behavior

resembles the decomposition behavior of rice hulls (Fig.

250

200

O 。150 ';;

L

コゼQ)

100E ω ト

ー守・ ー・・ーーーーーーー . . . . .

50

。)

O

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z

伊

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no

28

7

凋“Y

L

勺'』

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nu

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、J

-

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i

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〉、... てコ可コω Q)

E 15 ぎて3Q)

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'" 的 。

increased to pH 4 in the 3rd-5th fraction. The cause of the

decreased pH was considered to be released acetyl groups

from hemicellulose and organic acids produced by sec-

ondary decomposition of monosaccharides [8， 20]. After

that， pH increased gradually as the concentration of solu-

bilized products decreased in each fraction.

Figure 4 shows saccharification behavior of rice hulls.

In the 1st and 2nd fraction， saccharides were not obtained.

Then， after the 3rd fraction， when the temperature of

HCW reached over 1400

C， hydrolyzed products of hemi-

cellulose (arabinoxylan) were started to obtain， such as

xyloseαyl)， arabinose (Ara)， xylobioseα2)， and xylotri-

oseα3). After the temperature reached 2000

C (in 4th and

5th fraction)， these saccharides markedly produced.

However， after 6th fraction， these saccharides were not

obtained.

Furthermore， polymers of greater degree of polymeriza-

tion than xylotriose were also obtained， as shown in Fig. 5.

While， as for glucose and cellooligosaccharides， they were

hardly obtained in this treatment condition， meaning that

cellulose is not decomposed. Obtained solubilized saccha-

rides can use for food additives， functional foods and feed-

stocks for fermentation.

Fig. 4 Saccharification behavior of the rice hulls in血eprocess of

hydrothermal treatrnent 区~翠;Arabinose，・・・・ ;Galactose，

匹rrm田 ;Glucose，にここコ ;Xylose， i?ZZZ2l ; Xylobiose， f.:.:-:-:.:-:.:-:ヨ，

Xylo廿iose，ーーーーーー ;Temp

7

e、Jx

〉、

x hH一切CUHC目

250

200 (

O O

150 1:' コ+' 伺L C

100E 。ト

50

(l)HCSEω恥

oza

b

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r

D

A

a

守

ーーー ーーーーーーーーー・ー、. . . . .

30

K

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A

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G

nu

内

ζ

内

ζ

4

5

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(ωωmw』〉

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oeωc-万一ω一一』

ωパ

F03司OLa司

ωN=-』コ一。

ω

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v

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m

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1

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一nun

--内正

O&EL

、• n

H

ρしMw

&E

ρしMw

DH

10 。。3

8(Fr. No.) Lーー一一」28 32

『，，

au守

i2

po

nu

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)

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-au

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--

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ρ

h

V

4

一

m

一2T

J1

内‘

u

-LnMU

内

4

i4

。。

Fig.5 Typical HPAE-PAD chromatogram of solubilized products

at 200oC. Ara: Arabinose， Gal: Galactose， G1c; Glucose， Xyl;

Xylose， X2; Xylobiose， X3; Xylo廿iose.

Fig.3 Change in the solubilized products yield and the pH of

effluent in each fraction.区三ヨ;Solubilzed products yield，

一+ー;pH of effluent-ーーーーー ;Temp.

112 Satoshi KUMAGAI， Mayumi OTA， Sumi NAKANO， Nobuyuki HAYASHI， Tsuyoshi S必<AK¥，Yasuhiko KAIDA

10000

三 1000~

申O '-

bll 、:::t

E D

+"'

'" '-+"' C 申U E O O

100

10

0.1

0.01 2 3 4 5 6 7 8

Fraction number (4min/Fr.)

250

200

O 。150ω

Lーコ+"' 国

'-U

100E 由

ト

50

。

Fig. 6 Time course of metal (P， Al， K， Na and B ) concentration in

the process of hydrothermal trea凶lentof rice hulls.一+ー;P，

ー+ー ;Al，ー+ー ;K，ー#ー;Na，ー+ー;B，ーーー;Lower limit，

・ーー;Temp

2) and pH of effluent (Fig. 3). As mentioned above， the

decomposition product at 2000

C could be used for food

additives and functional foods. Hence， the removal of the

poisonous metals should be taken into consideration，

when rice hulls polluted by poisonous metals are used as

raw materials.

τne former metals (P， A!， K， Na and B) may simply exist

in the cell: consequently， these metals as eluted without

decomposition of cell wall. On the other hand， the latter

metals (Cd， Cu， Pb， Zn， As， Ca and Mg) may exist in the

cell wall as materials combined with organics chemically

or physically. As a result， it was necessary to decompose

the hemicellulose fraction to elute these metals.

That is to say， raising the purity of organic matter might

be possible by lengthening the time of the 1st仕actionand

inducing full elution to obtain high-quality organic matter

with few metals in the 4th and the 5th企actions.

4. Conclusions

The following results were noted in relation to the elu-

tion behavior of metals in the hydrothermal treatment pro-

cess at 200oC.

1) Concentration of solubilized products tended to

increase as the treatment temperature became higher.

The maximum yield of the solubilized products was the

4th仕action，when the HCW temperature reached 200oC.

Hemicellulose was hydrolyzed and solubilized mainly as

oligosaccharides.

1000 250

(

三100ω

200

U Lー

い、、bll

ミ〕

E o +"' 司'-+"' C U U c o O

10

0.1

0.01 2 3 4 5 6 7 8

Fraction number (4min/Fr.)

。。150 ~

'-コ+"' 回忌ーω a.

100 E ω ト

50

。

Fig. 7 Time course of metal( Cd， Cu， Pb， Zn， As， Ca and Mg)

concen甘ationin the process of hyd，rothermal treatment of riα

hulls.一+ー;Cd，ー+ー;Cu，ー唱ー ;Pb，一暢ー ;Zn，ー+ー;As，

一+ー;Ca，ー+ー ;Mg，ーーー ;1ρwer limit，ーーーーーー;Temp.

2) Although the pH of the initial effluents maintained

about pH 6， it decreased rapidly to pH 4 in the latter frac-

tions.τne cause of the pH decrease was considered to be

released acetyl groups from hemicellulose and produced

organic acids by secondary decomposition of monosac-

charides derived from hemicellulose.

3) Elution of heavy metals， alkaline earth metals， and arse-

nic depended upon the temperature. In contrast， alkali

metals， phosphorus， boron， and aluminum did not depend

upon the temperature， but rather on the treatment time.

References

[1] T. Sakaki， M. Shibata， T. Miki， H. Hirosue， N. Hayashi;

Decomposition of cellulose in near-critical water and fer

mentability of the products. Energy & Fuels， 10， 684-688

(1996) .

[2] T. Sakaki， M. Shibata， T. Miki， H. Hirosue， N. Hayashi;

Reaction model of cellulose decomposition in near critical

water and fermentation of products. Bioresour. Technol.， 58，

197-202 (1996)

[3] H. Ando， T. Sakaki， T. Kokusho， M. Shibata， Y. Uemura， Y.

Hatate; Decomposition behavior of plant biomass in hot-

compressed water. Ind. Eng. Chem. Res.， 39， 3688-3693

(2000).

[4] S. Kumagai， N. Hayashi， S. Fujita， T. Sakaki; Production

behavior of xylose組 dxylooligosaccharides from chinqua-

pin using a hot-compressed water treatment. ]. ]pn. Food

Eng.， 5， 205-210 (2004).

Elution Behavior of Metal国durin耳 Hydro世lermalDeωmposition of Li~nocellulosic Biomass 113

[5] S. Kumagai， N. Hayashi， S. Fujita， T. Sakaki， Y. Adachi; ]. Chem. Eng. ]pn.， 26， 676-680 (1993).

Production behavior of xylose and xylooligosaccharides [13] M. Sasaki. B. Kabyemela， R. Malaluan， S. Hirose， N. Takeda，

from chinquapin using a hot-compressed-water flow type T. Adschiri， K. Arai; Cellulose hydrolysis in subcritical

reactor.]. ]pn. Food Eng. 5， 243-248 (2004). and supercritical water. ]. Surpercrit. Fluids， 13， 261-268，

[6] S. Kumagai， N. Yamada， T. Sakaki， N. Hayashi; (1998).

Characteristics of hydrothermal decomposition and sacchar- [14] M. Sasaki， Z. Fang， Y. Fukushima， T. Adschiri， K. Arai;

凶cationof various lignocellulosic biomass and enzymatic Dissolution and hydrolysis of cellulose and subcritical water.

saccharification of the obtained hydrothermal-residue. ]. Ind. Eng. Chem. Res.， 39， 2883-2890 (2000).

]pn. Inst. Energy. 86， 712-717 (2007). [15] T. Okutani， Y. Nakata; Utilization of silica-accumulated

[7] N. Hayashi， S. Fujita， G. Irie， T. Sakaki， M. Shibata; Reaction plants as silica resource. NEW CERAMICS， 9， 35-44 (1992).

kinetics of cellulose decomposition in hot-compressed- [16] ]. P. Groten， P. ]. Bladeren; Cadmium bioavailability and

water.]. ]pn. Inst. Energy 83， 205-814 (2004). health risk in food. Trends in Food Science & Technology，

[8] S. Kumagai， N. Hayashi， T. Sakaki， N. Nakada， M. Shibata; 51，50-55 (1994).

Fractionation and saccharification of cellulose and hemicel- [17] ]. P. Bennett， E. Chiriboga，]. Coleman， D. M. Waller; Heavy

lulose in rice hull by hot-compressed-water treatment with metals in wild rice企omnorthern Wisconsin. The Sci. of出e

two-s句pheating.]. ]pn. Inst. Energy， 83， 776-781 (2004). To凶 Environment，246， 261-269α000).

[9] S. Kumagai， T. Sakaki， N. Hayashi; Solubilization of hemicel- [18] A Manu巴1，V. M. Teresa， M. Pedro;τbe influence of Cu

lulose in chinquapin by hot-compressed-water treatment， concentration on ethanolic fermentation by saccharomyc巴s

followed by enzymatic saccharification of the solubilized cerevisiae.]. Biosci. Bioeng.， 90， 163-167 (2000)

products. ]. ]pn. Food Eng. 6， 297-300α005). [19] S. I. Mussatto， I. C. Roberto; Alternatives for detoxification

[10] O. Bobleter， G. Bonn;百lehydrothermolysis of cellobiose of dilute-acid lignocellulosic hydrolyzates for use in fermen-

and its reaction-product D-glucose. Carbohydr. Res.， 124， tative processes. Bioresource Technol.， 93，1-10 (2004)

185-193 (1983). [20] S. Haghighat

「日本食品工学会誌J， Vo1. 9， No. 2， p. 114， ]un. 2008

く〉く〉く〉 和文要約 く〉く〉く>

リグノセルロース系バイオマスの水熱分解過程における

金属溶出挙動

熊谷聡 1，a，t 太田真由美 1 中野寿美 1 林信行 2 坂木剛 3 甲斐田泰彦 3

1純真短期大学食物栄養学科 2佐賀大学農学部生命機能科学科，

3産業技術総合研究所バイオマス研究センター

著者らは，高温高圧状態でかつ液体状態の水，すな

わち加圧熱水を反応媒体としたリグノセルロース系バ

イオマスの糖化方法について研究を行っている.その

中で，バイオマスを 2000

C付近の加圧熱水で処理するこ

とにより，ヘミセルロースが選択的に糖化され，とく

にへミセルロースが広葉樹や稲わら，麦わら，籾殻の

ようにキシラン系であるものからは，キシロオリゴ糖

が得られることが明らかとなった.

しかしながらノTイオマス中には，へミセルロースの

ような有機質だけでなく無機質(金属)も含まれており，

加圧熱水処理により得られた糖化物を食品関連素材と

して利用することを考えた場合，金属のなかには有害

なものがあることから，その溶出挙動も併せて調べる

必要がある.

(受付 2∞8年 1月29日，受理 2008年 5月 13日)

1干 815-8510 橋岡県福岡市南区筑紫丘 1-1-1

2〒 840-8502 佐賀県佐賀市本庄町 1

3〒841-0052 佐賀県鳥栖市宿町 807-1

a現所属。 佐賀大学農学部 (84仏8502 佐賀県佐賀市本庄町 1)

tF拡 ω2-552-2707，E-mail: kumagais@hotmail.co.jp

そこで，本論文では，バイオマスの一例としてモミ

ガラを原料とし，パーコレータ型反応器を用い， 2000

C

までの加圧熱水で処理し，溶出される金属の挙動につ

いて調べた.

その結果，重金属，アルカリ土類金属，ヒ素の溶出

に関しては，まず室温処理で籾殻表面の遊離性金属が

溶出したのち， -8減少し，温度が上昇するにつれて，

再び溶出しはじめ，熱水温度が 2000

Cに達した第 4フラ

クションまたは第 5フラクションで最大値をしめした

後，漸減する傾向を示す乙とがわかった.

一方でアルカリ金属， リン，ホウ素，アルミニウム

の溶出に関しては，明瞭な温度依存性が認められず，

時間にのみ依存して少しずつ溶出する傾向を示すこと

がわかった.