JARQ 38 (4), 275 279 (2004) http://www.jircas.affrc.go.

jp

Chlorine-Free Bleaching of Kraft Pulp from Oil Palm

Empty Fruit Bunches

Ryohei TANAKA1*, WAN ROSLI W. D.2, Kengo MAGARA3,

Tsutomu IKEDA4 and Shuji HOSOYA3
1
Forestry Division, Japan International Research Center for Agricultural Sciences (JIRCAS)
(Tsukuba, Ibaraki 3058686, Japan)
2
School of Industrial Technology, Universiti Sains Malaysia
(Penang 11800, Malaysia)
3
Department of Chemical Utilization, Forestry and Forest Products Research Institute
(Tsukuba, Ibaraki 3058687, Japan)
4
Institute of Agricultural and Forest Engineering, University of Tsukuba
(Tsukuba, Ibaraki 3050006, Japan)

Abstract
Chlorine-free bleaching was carried out on kraft pulp from oil palm empty fruit bunches (EFB) with an
oxygen (O2) - acid (H2SO4) - ozone (O3) - hydrogen peroxide (H2O2) bleaching sequence. The -num-
ber (= an indicator of lignin content) of the pulp was reduced considerably after these processes indi-
cating that most of the lignin present in the pulp can be removed using this chlorine-free sequence.
Handsheets of both bleached and unbleached EFB pulp were prepared and their paper properties were
determined. Brightness, a measure of the whiteness of paper, was achieved to ca. 75% for the bleached
EFB pulp, showing a possibility of achieving 80% of brightness by chlorine-free bleaching. Paper
strengths as indicated by tensile, tear and burst indices as well as stretch did not show significant dif-
ferences between before and after bleaching. It is notable that these results were obtained despite a
large decrease in viscosity by the bleaching process. Moreover, the EFB bleached pulp showed com-
parable strengths to hardwood pulps, indicating that EFB has the potential as a raw material for chemi-
cal pulp production using chlorine-free bleaching sequences.

Discipline: Forestry and forest products

Additional key words: EFB, oxygen, ozone, brightness, paper strengths

tively.
Introduction In Malaysia, the largest producer in the world, total
area of oil palm plantation is close to 3.2 million ha,
Oil palm, Elaeis guineensis, produces palm oil (PO) which accounts for almost 50% of the land under
and palm kernel oil (PKO), which are widely used in cultivation6. Although oil from the palm tree is an excel-
food and other industries such as detergents and cosmet- lent product for the country, its lignocellulosic residues
ics. Total production of the palm oils is 24.5 million t/y have not been effectively used. One of the most abun-
in the world, which accounted for more than 20% of total dant residues is empty fruit bunches (EFB), which are left
oil and fats production in 20009. Large producers are behind after removal of oil palm fruits for the oil refining
Malaysia, Indonesia and Nigeria, which share 47%, 34% process. Tons of EFB are regularly discharged from palm
and 4.2% of the world production of PO + PKO, respec- oil refineries, amounting to 12.4 million t/y (fresh

This paper reports the results obtained in a collaboration research work on Studies on the development of methods for the use of
underutilized timber resources in the tropics between Japan International Research Center for Agricultural Sciences and Universiti
Sains Malaysia.
Present addresses:
1,4
Department of Chemical Utilization, Forestry and Forest Products Research Institute
(Tsukuba, Ibaraki 3058687, Japan)
*Corresponding author: fax +81298743720; e-mail ryohei@affrc.go.jp
Received 22 October 2003; accepted 14 May 2004.

275
R. Tanaka et al.

weight) 3, some of which are used as fuel, however, most method of TAPPI Standard T230 su-66), respectively.
of them are left unused.
To increase the added value of these residues, sev- 3. Bleaching
eral investigations have been carried out to produce The chlorine-free bleaching process studied here
papermaking pulp from EFB by chemical and mechanical includes four sequential steps of oxygen, acid, ozone and
pulping processes1,2,4,7,12. It is quite reasonable to produce hydrogen peroxide bleaching at a pulp consistency of
pulp from the lignocellulosic residues for papermaking. 10% (medium consistency).
Consumption of paper is increasing dramatically in South Oxygen (O2) bleaching was carried out using a Mark
East Asian countries including Malaysia, nevertheless a V High-Intensity Mixer (Quantum Technologies, Inc.,
huge amount of EFB are left unused in those palm oil- U.S.A.) under alkaline conditions by addition of 1%
producing countries. NaOH (w/w) aqueous solution. Magnesium sulfate
Although several studies have been carried out on (0.1%) was also added as a protection reagent for cellu-
EFB pulping, investigation on pulp bleachability is lim- lose. Reaction temperature and O2 pressure were main-
ited. Due to increased awareness of the danger associ- tained at 95C and 5 kg/cm2, respectively. The total
ated with the usage of chlorine and its derivatives, it is reaction time was 40 min with occasional mixing.
now necessary to utilize elemental chlorine-free (ECF) or The acid bleaching process was performed in a
totally chlorine-free (TCF) bleaching sequences for pulp. water bath at 100C for 60 min. A heat-resistant plastic
Once this oil palm by-product becomes a raw material for bag was used for the reaction. The pulp was treated in a
pulp production, it will be essential to have chlorine-free buffer solution of pH 2, adjusted by addition of 4N
bleaching processes in the future. In this study, kraft H2SO4. Effluent of the acid bleaching was analyzed by
pulping was carried out for an EFB sample under several HPLC as described in a previous paper5.
different pulping conditions and chlorine-free bleaching For ozone (O3) bleaching, the same mixer for the O2
was applied to the EFB kraft pulp. bleaching was used, together with an ozone cart. Total
amount of O3 added was 0.5% on pulp. Reaction temper-
Materials and Methods ature was maintained at 20C for a total reaction time of
2.5 min with occasional mixing.
1. Material For hydrogen peroxide (H2O2) bleaching, pulp slurry
The EFB sample used in this study was in the form of 10% consistency (adjusted using 0.05N NaOH aque-
of fibrous strands. It was supplied by SABUTEK (M) ous solution) was placed in a plastic bag and a corre-
SDN BHD, Malaysia. It had already been manufactured sponding amount of 1% or 2% H2O2 was added. Then
by the company, including the processes of defibrization, the reaction was carried out at 80C for 120 min in a
washing, cleaning, sorting and drying. The sample water bath. A small amount (ca. 0.6% on pulp) of a sta-
strands were used as received. Moisture content of the bilizing agent Dequest 2066 (sodium salt of diethylenetri-
fibrous strands was determined to be 9.5%. amine-penta (methylene phosphonic) acid, Monsanto
Japan Ltd.) was also added to the pulp.
2. Kraft pulping (KP)
Kraft pulping was carried out using 4-L or 2-L auto- 4. Determination of handsheet properties
claves manufactured by NAC Autoclave Co., Ltd., Japan. From the bleached and unbleached KP, handsheets
Four pulping conditions were selected as shown in Table were prepared and conditioned at 20C and 65% relative
1. After each cooking, the pulp was washed and screened humidity (RH) according to JIS P8111. Physical and
through a 0.2 mm slit (8-cut). Kappa () number and mechanical properties of the handsheets were evaluated
pulp viscosity were determined according to TAPPI Stan- according to appropriate JIS standards.
dard T236m-60 and JPRI Standard 3015 (a modified

Table 1. Pulping conditions of EFB

Condition Active alkali Sulphidity Liquor to Cooking temp. Time to T Time at T

(%) (%) EFB ratio (T, C) (min) (min)
I 16 25 10 170 90 90
II 14 25 10 170 90 90
III 16 25 10 160 90 120
IV 16 25 8 170 90 90

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 Chlorine-Free Bleaching of Oil Palm EFB Pulps

Results and Discussion gest reduction after O3 and H2O2 bleaching. It is also
obvious that the decrease in -number after O2 bleaching
Yields and properties of EFB kraft pulp prepared in is rather small in comparison with O3 bleaching suggest-
this study are given in Table 2. Referring to Table 1, it is ing the powerful oxidant nature of the latter. This is fur-
evident that the active alkali concentration is the most ther confirmed by the viscosity data, which showed a
effective factor on the yield and properties, compared to relatively small decrease when using O2 but a significant
liquor/EFB ratio, cooking temperature and cooking time. reduction with O3. During ozone bleaching, there is not
A reduction of 2% in active alkali substantially increased only a substantial removal of lignin but also an occur-
the -number and amount of screenings when the condi- rence of attack on cellulose, which is reflected in the vis-
tions I and II were compared. Liquor to EFB ratio and cosity values.
cooking temperatures did not show any crucial changes By HPLC analysis of the effluent after the acid
except pulp viscosity. When considering -number in bleaching, the presence of 2-furancarboxylic acid and 5-
relation to viscosity, the condition III may be the most formyl-2-furancarboxylic acid was indicated. These two
desirable one. Overall, the pulps prepared under the compounds are acid-degraded products of hexeneuronic
given conditions had relatively low -numbers with high acid which can be formed from 4-O-methylglucuronic
viscosity values, which indicates that lignin content of acid groups in xylan of softwood and hardwood KPs5.
each pulp was relatively low and the degree of polymer- The result obtained here may indicate the presence of 4-
ization (DP) of cellulose remained at an acceptable level. O-methylglucuronic acid groups in xylan of EFB KP.
Due to the limited availability of pulps prepared, all pulps Moreover, the presence of hexeneuronic acid contributes
prepared under the conditions I, III and IV were mixed to an increase in -number of the pulp. Total amount of
together for being used in the bleaching process; the pulp the acid-degraded products was calculated to be 0.68
prepared under the condition II was not considered mmol/100 g pulp, which corresponds to 0.58 in -
because of its high -number. The -number and viscos- number5. This is in good agreement with the reduction of
ity of the mixed pulp were determined to be 14.9 and -number from 11.0 to 10.3 after the acid bleaching as
23.9, respectively. shown in Table 3. It means that the acid bleaching pro-
Results for the bleaching process are shown in Table cess had only degraded hexeneuronic acid in the EFB KP
3. There is a small but gradual decrease in -number without the removal of lignin. The degradation does only
until the end of the second bleaching stage, i.e. acid occur under acidic condition and hexeneuronic acid is
bleaching, after which the decrease became more signifi- assumed to be mostly removed during this process. The
cant by applying the ozone sequence. Pulp viscosity was above result indicates that the contribution of hexeneu-
also reduced in each subsequent sequence with the big- ronic acid to -number is almost negligible for this EFB

Table 2. Yields and pulp properties of EFB kraft pulps

Condition Yield (%) Screened yield (%) Screenings (%) -number Viscosity (cp)
I 44.4 43.7 0.65 14.2 19.7
II 45.4 42.0 3.42 25.8 23.2
III 44.6 43.1 1.50 15.8 27.5
IV 44.4 42.6 1.78 18.7 30.2
I,III,IV mix 14.9 23.9

Table 3. Bleaching of EFB kraft pulp

Sequence -number Viscosity (cp)

unbleached 14.9 23.9
O2 11.0 22.0
O2 / acid 10.3 21.2
O2 / acid / O3 3.33 16.6
O2 / acid / O3 / H2O2 1% * 11.6
O2 / acid / O3 / H2O2 2% * 11.2
*Not determined.

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R. Tanaka et al.

Table 4. Handsheet properties of EFB kraft pulp

Bleaching sequence Unbleached O2 / Acid / O3 O2 / Acid / O3 / H2O2 1% O2 / Acid / O3 / H2O2 2%

-number 14.9 3.33 * *
Viscosity (cp) 23.9 16.6 11.6 11.2
Freeness (mL) 240 240 230 238
Basis weight (g/m2) 63.5 59.4 59.6 58.0
Density (g/cm3) 0.77 0.78 0.82 0.81
Tensile index (N m/g) 67.3 67.5 67.7 63.9
Stretch (%) 4.87 5.88 5.81 4.98
Tear index (mN m2/g) 12.5 13.0 12.5 11.7
Burst index (kPa m2/g) 5.33 5.60 5.39 5.05
Folding (MIT, 1 kg) 1,272 1,518 1,160 1,115
Brightness (%) 27.6 55.3 73.2 73.9
Opacity (%) 98.4 85.6 74.4 72.4
*Not determined.

6 KP.
Handsheet properties of bleached and unbleached
5
Burst index

pulp are shown in Table 4. Handsheets of bleached pulp

(kPa m2/g)

4 were produced before and after the H2O2 bleaching.

Compared with the unbleached pulp, there were no sig-
3 nificant losses in paper strengths by the bleaching
sequences, which are indicated by tensile, tear and burst
0 indices and stretch. A marginal decrease was observed
20 for folding strength of each pulp after the bleaching.
Brightness of the pulp with O2 / acid / O3 / H2O2
15 bleaching reached 7374%. Khoo and Lee achieved the
Tear index
(mN m2/g)

brightness of 80% for an EFB kraft pulp by a chlorine-

10 based bleaching process7. Although values of brightness
obtained by the chlorine-free bleaching are still lower
5
than that achieved by the chlorine-based bleaching, there
0 is a great potential for the chlorine-free bleaching process
to achieve almost the same level in bleachability as chlo-
80 rine-based bleaching for EFB pulp. It is also interesting
to note that after the H2O2 sequence, the brightness has
70
Tensile index

been increased drastically whilst maintaining the paper

(N m/g)

60 strengths at acceptable levels. Opacity, which is the abil-

ity of paper to hide or mask a color or object in back of
50 the sheet, obtained for the bleached handsheet in this
study is found to be at a comparable level with that of a
0 hardwood KP, which has almost the same value in
500 400 300 200 100
brightness8.
Freeness (CSF, mL)
Tensile, tear and burst strengths of EFB handsheets
are plotted against freeness (CSF: Canadian Standard
Fig. 1. Paper properties of EFB and hardwood kraft pulps
Freeness) as shown in Fig. 1. Literature values of EFB
: data from the experiment.
: data from the references for EFB KPs7. KP with chlorine bleaching7 and hardwood KP11 are also
: data from the references for hardwood KPs11. plotted in this figure for comparison, although there is no
Open symbols: bleached. comparable pulp data from the references that have
Closed symbols: unbleached. almost the same level of freeness as the EFB pulps stud-

278 JARQ 38 (4) 2004

 Chlorine-Free Bleaching of Oil Palm EFB Pulps

ied here. In general, tensile and burst indices are depen- perspective, eds. Singh, G. et al., Malaysian Oil Palm
dent on the freeness for the same pulp, i.e. the lower the Growers Council, Kuala Lumpur, Malaysia, 4153.
4. Guritno, P. et al. (1995) Utilisation of oil palm empty fruit
freeness is, the higher the indices are7,10. In contrast, the
bunches for kraft paper production. In Proceedings: 3rd
freeness has less of a contribution to tear index7, or has an national seminar on utilisation of oil palm tree and other
opposed effect to the index10. The tensile and burst indi- palms 1994, eds. Koh, M. P. et al., Oil Palm Fibre Utilisa-
ces plotted in Fig. 1 exhibited almost linear increases tion Committee, Kuala Lumpur, Malaysia, 163168.
along the decreases of the freeness. For the tear index, 5. Ikeda, T. et al. (1999) Sulfuric acid bleaching of kraft
the freeness dependence was not observed, which pulp III: Reactivity of kraft pulping resistant structures
under acidic conditions. J. Wood Sci., 45, 417424.
resulted in a similar trend with data of the above-men-
6. Ismail, F. (2000) Focus Oil palm sector turns over a
tioned references7,10. These results indicate that the EFB new leaf. New Sunday Times 2nd April 2000, Malaysia.
pulps prepared in this study show comparable properties 7. Khoo, K. C. & Lee, T. W. (1991) Pulp and paper from the
with hardwood kraft pulps. Moreover, the non-chlorine oil palm. Appita J., 44, 385388.
bleaching processes examined in this study may work 8. Magara, K., Takano, I. & Hosoya, S. (1997) Ozone
bleaching of kraft pulp. Kami-parupu gijutu kyokai-shi
almost the same as a chlorine-contained process on EFB
(Jpn. TAPPI J.), 51, 19081915 [In Japanese with
pulps. It suggests that EFB kraft pulp is able to produce English summary].
paper sheets with the same strength level as hardwood 9. Malaysian Palm Oil Board (MPOB) Statistical data of
pulp by using an environmentally friendly method. world production of 17 oils and fats. Available online at
http://mpob.gov.my/ (verified 1 October 2003).
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