Conference topic 7. PULP & PAPER

Eucalyptus globulus heartwood and its influence in kinetics of pulp production

Ana LOURENÇO, Jorge GOMINHO, Helena PEREIRA

Universidade Técnica de Lisboa (UTL), Lisboa; Instituto Superior de Agronomia (ISA); Centro de Estudos

Florestais (CEF); analourenco@isa.utl.pt

Abstract

Eucalyptus globulus is the most species used in Peninsula Iberica for pulping, due to its

anatomical and chemical characteristics, in particular its low lignin content. In this context

the aim of this work was to study the influence of heartwood from E. globulus during the

pulping process. For this purpose a tree with 18 years was chosen due to its higher

extractives content in heartwood compared to sapwood (9.8 % vs. 3.9 %) and a total lignin

content of respectively, 23.5% and 24.3 %. The study was developed using three

temperatures (130, 150, 170 ºC) and pulps were produced with several cooking times (1 to

95 min). The liquor was produced in the laboratory with 30 % sulfidity, 20 % alkali active

and liquor to wood ratio of 4:1. Pulps were analysed in respect to total yield and residual

lignin, and two kinetic models were applied to explain heartwood and sapwood

delignification.

During the heating stage of pulping the mass loss was considerable, i.e for heartwood

represented from 23.7 to 31.8%, and for sapwood, 15.4 to 23.5%. This mass included

removal of lignin, as well as solubilization of wood extractives which are in great amount

in heartwood. In fact, the presence of higher extractives enables a faster removal of lignin

in heartwood at a given pulping time, but in the end, and in particular to 170ºC, the

residual lignin in the heartwood and sapwood pulps were quite similar (2.0 % and 1.1 %).

The larger differences between sapwood and heartwood were obtained during

delignification at 130ºC with 8% higher final yield for sapwood, but this difference

decrease to half in pulps from 150 and 170ºC cooking temperature. The modelling results

showed that: i) the kinetics parameters were similar in heartwood and sapwood

delignification at all temperatures; ii) both models were quite adequate for the material

used, with good correlations (higher than 0.99); iii) heartwood presence does not influence

the kinetic development in relation to delignification since no major differences in the

parameters values were noticed.

Key words: Eucalyptus globulus; heartwood; delignification; kinetics

Lourenço, A, Gominho, J, Pereira, H. Eucalyptus globulus heartwood and its influence in kinetics of pulp production. IUFRO Conference 2012. Division 5 Forest Products, Topic 7. Pulp & Paper, Estoril, Lisbon, Portugal, 8-13 July 2012. Oral presentation.

Eucalyptus globulus heartwood and its influence in kinetics of pulp production

Ana Lourenço, Jorge Gominho, Helena Pereira

Introduction

Aim of the work

Study the influence of heartwood from Eucalyptus globulus during pulping Why? Eucalyptus globulus is mostly used for pulping Heartwood has more extractives

Extractives causes negative impact in delignification process

Eucalyptus globulus

Eucalyptus globulus is a species with rapid growth, used for pulping due to its characteristics:

Chemical: low extractives content (1.9-9.7%) lignin (18-21%) – GS lignin cellulose (40-53%) Anatomical fibre: length (0.87 mm to 1.04 mm) width (21.3 µm) wall thickness (5.7 µm)

Sapwood: living cells circulation of nutrients from roots to leaves brighter than heartwood less extractives content

Heartwood and sapwood

Heartwood: dead cells inner wood more dense less permeable compared to sapwood high resistance to biological attack

(Stained)

Heartwood and pulping

Heartwood influence in pulp production Since heartwood has more extractives than sapwood is expected that:

More mass is lost, so pulps with low yield

More consumption of reagents

Less lignin extraction

Pulps less brighter

More consumption of bleaching reagents

Pitch problems

What really happens during pulping? Studies of delignification can explain this. Two kinetics approaches were used.

Delignification studies

𝐿

𝐿0= 𝑎𝑖 exp −𝑘𝑖 ∗ 𝑡 + 𝑘𝑏 exp −𝑘𝑏 ∗ 𝑡 + 𝑎𝑟 exp(−𝑘𝑟 ∗ 𝑡)

2,0

3,0

4,0

5,0

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

ln (

L/L0

)

Residual (r)

Bulk (b)

Initial (i)

Initial (i) Bulk (b) Residual (r)

Consecutive approach

Lignin removal due to different linkages corresponding to different phases: - initial (20-25% lignin removal) - bulk (70% ) - residual

Delignification studies

Heartwood

Time (min)

01 3 5 10 15 20 25 35 50 65 80 95

ln (

L)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

L1+2 lignin fractions

L1 lignin fraction

𝐿 = 𝐿1,0 ∗ (1 − exp(− 𝑘1𝑡)) + 𝐿2,0 ∗ (1 − exp −𝑘2𝑡 )

More reactive lignin Less reactive lignin

𝑘2 = ln𝐿2,0

𝐿𝑡/(𝑡𝑡 − 𝑡2)

𝐿𝑛,𝑡 = 𝐿2,0 ∗ (exp −𝑘2𝑡 )

Simultaneous approach

No phases, but lignin fractions The different linkages are break at the same time but with different

velocities

Material and Methods

Raw material preparation

Eucalyptus globulus with 18 years was chosen due to its higher extractives content in

heartwood (9.8%)

sapwood (3.9%)

Material was ground and sieved

The 40-60 mesh used for chemical characterization

Kraft Pulping

Fraction 20-40 mesh used for delignification process (to reduce diffusion problems) Kraft conditions:

Sulfidity: 30% (as Na2O) Alkali active: 20% (as Na2O) Liquor to wood ratio: 4:1 Temperatures: 130ºC, 150ºC, 170ºC

Several cooking times from 0 to 180 min, with 5 min to reach temperature

Determination of total yield and total lignin (Klason and soluble

using TAPPI standards)

Results

Pulp yield

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

Yie

ld (

%)

40

50

60

70

80

90

100H 130 ºC

S 130 ºC

H 150 ºC

S 150 ºC

H 170 ºC

S 170 ºC

8%

4%

4%

Modeling

Consecutive model Only two phases were identified

At each temperature the values of reactions rates for each lignin

were similar for sapwood and heartwood

Heartwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

To

tal

lig

nin

(%

)

0

20

40

60

80

100130 ºC experimental

150 ºC experimental

170 ºC experimental

130 ºC model

150 ºC model

170 ºC model

Sapwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

To

tal

lig

nin

(%

)

0

20

40

60

80

100130 ºC experimental

150 ºC experimental

170 ºC experimental

130 ºC model

150 ºC model

170 ºC model

Simultaneous model Two reactive types of lignin were identified for 130ºC and 150ºC, and

three types for 170ºC

At each temperature the values of reactions rates for each lignin were similar for sapwood and heartwood

Modeling

Heartwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

To

tal

lig

nin

(%

)

0

20

40

60

80

100130 ºC experimental

150 ºC experimental

170 ºC experimental

130 ºC model

150 ºC model

170 ºC model

Sapwood

Time (min)

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

To

tal

lig

nin

(%

)

0

20

40

60

80

100130ºC experimental

150ºC experimental

170ºC experimental

130ºC model

150ºC model

170ºC model

Experimental vs. Predicted The two models explain very well the lignin reaction kinetics in the range

of temperatures tested

Heartwood and sapwood presented very small differences in respect to delignification kinetics

Modeling

Consecutive

Experimental data (%)

0 20 40 60 80 100

Mo

de

l p

re

dic

tio

ns

(%

)

0

20

40

60

80

100H 130 ºC

S 130 ºC

H 150 ºC

S 150 ºC

H 170 ºC

S 170 ºC

Simultaneous

Experimental data (%)

0 20 40 60 80 100

Mo

de

l p

re

dic

tio

ns

(%

)

0

20

40

60

80

100H 130 ºC

S 130 ºC

H 150 ºC

S 150 ºC

H 170 ºC

S 170 ºC

Conclusions

Conclusions

Heartwood delignification under kraft conditions was similar to

sapwood

But heartwood has more extractives which presence reduces pulp yield (heartwood obtained 4% less yield compared to sapwood)

Heartwood presence did not influence the kinetic development of the pulping process, regarding delignification

In respect to the delignification models:

- the kinetic parameters were similar in heartwood and

sapwood

- both models could be used, with good correlations between experimental data and predicted values

Deliverables

“Modeling of sapwood and heartwood delignification kinetics of Eucalyptus globulus using consecutive and simultaneous approaches”

Lourenço, A, Gominho, J, Pereira, H. 2011. Journal Wood Science 57: 20-26.

“Pulping and delignification of sapwood and heartwood delignification from Eucalyptus globulus”

Lourenço, A, Gominho, J, Pereira, H. 2010. Journal of Paper and Paper Science 36(3-4): 85-90.

Acknowledgments

The authors thank: Clara Araújo and Altri, who supplied the raw material FCT through a PhD Scholarship granted to the first author FECER/POCTI Programme

Thanks!

analourenco@isa.utl.pt