Effect of Cooking Liquor Ratio on Lignin Reduction in Pulping Process

from Cogongrass and Lemongrassleaves using Soda Process

Rosdanelli Hasibuan

, Leonardo Ginting

, Sasro Arif Purba

Chemical Engineering Department, Engineering Faculty, University of North Sumatera

Keywords: Alpha cellulose, lignin, cogongrass, lemongrass leaves, soda process

Abstract: Pulp is the raw material for paper making. The quality of pulp is determined by the content of cellulose and

the remaining lignin contained in the pulp. Alpha cellulose is a parameter used to determine the amount of

cellulose contained in the pulp. The alpha cellulose content in the pulp is affected by the concentration of the

cooking liquor. The level of lignin in the pulp shows the residual lignin left from incomplete hydrolysis. This

study aims to reduce the amount of lignin in the pulping process from cogongrass and lemongrass leaves using

soda process. The liquor that is used for cooking process is sodium hydroxide (NaOH) and sodium carbonate

(Na

) with a cooking time of 120 minutes, at a temperature of 110

C, with ratios of cooking liquor and

raw materials variation such as 1:1, 2:1, 3:1, and 4:1. The results of this investigation shows thatthe best

cooking conditionwas obtained in the ratio of cooking liquor and raw material 4:1 with alphacellulose content

83.11%, 56.31% ofyield, 0.78% ofash content, and Kappa number which is a method to determine the amount

of lignin remaining in pulp of 13.17, while the highest yield of 78.33% was obtained in the ratio of cooking

solution 2: 1. In spite of that, almost all produced pulp in this study has pulp quality in accordance with SNI

7274 and the Center of Pulp (alpha cellulose content > 40%, ash content <3%, and Kappa number 13.5).

1 INTRODUCTION

The need for pulp in Indonesia has increasedover the

years as the demand for paper keep increasing. The

government, through the Industrial Research and

Development Body (BPPI), encourages increasing

the production of pulp and paper from non-wood raw

materials because Indonesia has a large potential of

non-wood materials.

Head of the Center of Pulp and Paper, Andono

Sugiharto, said that Indonesia currently ranks 6th as

the world's paper producing country and 9th at world

pulp producer (Pikiran Rakyat, 2017). So far, most of

the raw materials for producing pulp were made of

wood, this can be seen from the total production of

4.55 million tons of pulp in 2013, only 18,680 tons or

0.0004% that is the pulp made of bamboo plants.

Other types of non-wood plants that are easily

obtained and can be used as raw material for pulping

include hemp, cotton, agricultural waste such as

bagasse, pineapple skin, rice straw, lemongrass and

various types of grasses and reeds (Yandha and

Sherren 2014) . The use of non-wood raw materials

has advantages, such as the potential is quite high,

easily made into pulp, easily milled, and easily

bleached with environmentally friendly materials.

This study uses cogongrass and lemongrass leaves as

raw material, mainly because cogongrass and

lemongrass leaves possess high cellulose content.

Besides, cogongrass also has become undesired

plants which is grown in the midst of other productive

plants so that they are always eradicated using

cogongrass poisonwhich can also damage the

environment.

The use of reeds which are difficult to eradicate

and lemongrass leaves as agricultural waste that has

not yet been used as raw material for pulp contribute

to become a good solutions in environmental

management. One of the factors that influence the

pulping process is the concentration of cooking

liquor, namely the right ratio between the cooking

liquor and the raw material. In this study, the ratio

between the cooking solution and the raw material

were 1: 1, 2: 1, 3: 1 and 4: 1 with 1: 1 ratio of

cogongrass and lemongrass leaves to obtained good

quality pulp.

378

Hasibuan, R., Ginting, L. and Purba, S.

Effect of Cooking Liquor Ratio on Lignin Reduction in Pulping Process from Cogongrass and Lemongrassleaves using Soda Process.

DOI: 10.5220/0010100603780383

In Proceedings of the International Conference of Science, Technology, Engineering, Environmental and Ramiﬁcation Researches (ICOSTEERR 2018) - Research in Industry 4.0, pages

378-383

ISBN: 978-989-758-449-7

2 LITERATURE REVIEW

2.1 Cogongrass

Raw materials used in pulp making usually are

woods, but non-wood raw materials can also be used.

One of them is cogongrass. Imperata cylindrica is

also known as japgrass, bladygrass, speargrass, reeds

and weeds. This plant is extremely easy to grow and

develop, and is widely distributed in tropical and

subtropical regions. Until now, this plant can be

found in more than 73 countries.

Because of the short growth cycles, abundant,

unsuitable to become animal feed and the lack of

commercial application of this grass, this plant can be

proposed as an alternative fiber in the pulp and paper

industry to reduce or replace the use of pure pulp

widely (Kassim et al, 2015).

Imperata has an alpha cellulose content of

40.22%, hemicellulose (pentosan) 18.40% and lignin

31.29% (Sutya et al, 2015). The cellulose content of

more than 40% (Kartikasari et al, 2015), making this

plant has a huge potential as raw material for pulp

making.

2.2 Lemongrass

Lemongrass is a plant that has its own commodity

which results in many plants being used as

agricultural crops. Lemongrass which is used or sold

in the form of lemongrass stems, causing lemongrass

leaves become waste. Lemongrass leaves contain

quite highcellulose content, so that it can be used as

an alternative material for pulp making.

2.3 Cellulose and Lignin

2.3.1 Cellulose

Cellulose is mostly found in cell walls and woody

parts of plants. Cellulose has a role that determines

the character of fiber and allows its use in paper

making. In pulping, fibers are expected to have high

cellulose content. The properties of materials

containing cellulose are related to the degree of

polymerization of cellulose molecules. Reduced

molecular weight below a certain level will cause

reduced strength. Cellulose fibers show a number of

properties that meet paper-making needs. The best

balance of papermaking properties occurs when most

lignins are excluded from fibers. Fiber toughness is

mainly determined by the raw material and the

process used in pulping (Surest and Dody, 2010).

2.3.2 Lignin

Lignin is the third macromolecule found in biomass,

functions as a binder between fibers. Lignin can be

removed from cell wall material which is insoluble

with chlorine dioxide.

The molecular structure of lignin is very different

when compared to polysaccharides, because it

consists of an aromatic system composed of propane

phenyl units. The properties of lignin are insoluble in

water and strong mineral acids, dissolve in organic

solvents and dilute alkaline solutions. The lignin

attached to the pulp product decreases the strength of

the paper and causes the paper to turn yellow.

The pulp will have good physical properties or

strength if it contains just a little lignin. This is

because lignin is water-repellent and stiff, making it

difficult for the grinding process. The lignin content

for wood raw materials is 20-35%, while for non-

wood materials is lower (Surest and Dody, 2010).

2.4 Pulp Making Process

2.4.1 Sulfate Process (Kraft)

In the Kraft process, sodium hydroxide and sodium

sulfide are used in wood pulp. This process is widely

used in the pulp and paper industry. In the Kraft

process, about half of the wood is dissolved in

chemicals and will form black liquor. This liquid is

cleaned from pulp by washing and being incorporated

into the Kraft renewal system where pulp inorganic

chemicals are recycled and reused, whereas in

dissolved organic matter can be used to produce

steam and energy (Tran and Vakkileinnen, 2011).

2.4.2 Sulfite Process

The sulfite process uses a cooking liquor in the form

of an acid which is a combination of acids mixed with

magnesium bisulfate. In this process, the cooking

liquor enters the wood and decomposes the lignin

which when cooked is converted into water-soluble

compound that can be washed (Sappi, 2003).

2.4.3 Soda Process

The soda process involves heating the fiber in a

pressurized reactor at a temperature of 100-170 °C

using 13-16% sodium hydroxide which is the cooking

liquor. The ratio of cooking liquor to dry fiber is 5:1.

In this process, lignin is separated from cellulose and

suspended in a liquid phase. In liquid phase which is

black liquor is separated from solid phase containing

Effect of Cooking Liquor Ratio on Lignin Reduction in Pulping Process from Cogongrass and Lemongrassleaves using Soda Process

379

cellulose due to lignin. This solid phase containing

cellulose is called pulp. The resulting pulp is then

processed in the manufacture of paper, boards,

composite materials, polymers and others. This black

liquor contains lignin and sodium hydroxide (soda)

which are usually further processed to be recycled

and reused in the process (Doherty and Thomas,

2006).

2.5 Factors Affecting Pulp Making

2.5.1 Cooking Liquor Concentration

The higher the concentration of cooking liquor, the

greater the amount of cooking liquor that reacts with

lignin, but the use of excess cooking liquor is not

good because it will cause the cellulose to degrade, so

that the cooking solution ratio must be in accordance

with the portion (proportional).

2.5.2 Ratio of Cooking Liquor to Material

The ratio of cooking liquor to raw material must be

sufficient so that the lignin fragments are perfect in

the degradation process and can dissolve completely

in the cooking liquor. Ratios that are too small can

cause redeposition of lignin so that it can increase the

Kappa number (the quality of the pulp decreases).

2.5.3 Cooking Temperature

Cooking temperature is related to the reaction rate

which can increase the rate of delignification

(removal of lignin), but at temperatures above 180

causes degradation of cellulose which at this

temperature lignin has been dissolved. Then the

optimum temperature ranges from 80-140

C [10].

2.5.4 Cooking Time

The longer the cooking time will cause the lignin

hydrolysis reaction to increase. However, cooking

time that is too long will cause cellulose to hydrolyze,

thus reducing the quality of the pulp. For cooking

before 1 hour the pulp has not been formed and for 5

hours of cooking the cellulose are degraded. The

optimum time in the delignification process is around

60-120 minutes with a constant lignin content in that

time span (Putra, 2012).

3 RESEARCH METHODOLOGY

3.1 Materials and Equipments

The raw material in the form of cogongrass and

lemongrass leaves with a ratio of 1: 1.

Cooking solution of 12.5% (NaOH and Na

) with

a ratio of 85% NaOH and 15% Na

and the

remaining is water (87.5%) (TAPPI, 1999).

3.2 Equipments

Set of Equipments

The set of equipmentsused in the research (Figure 1)

Figure 1: Series of Equipments in Pulp Making

Caption:

1. Barometer 7. MotorReducer

2. Thermometer 8. Driving motor

3. Safety valve 9. Digester

4. Gas holder

5. Fire heater

6. Driving connector with digester

3.3 Analysis

The analysis was carried out based on SNI 2009 and

TAPPI 1999 namely:

Analysis of Water Content of Raw Materials

Analysis ofAsh Content

Analysis of alpha, beta and gamma cellulose content

Analysis of Kappa Numbers

Analysis of Yield

ICOSTEERR 2018 - International Conference of Science, Technology, Engineering, Environmental and Ramiﬁcation Researches

380

3.4 Main Procedure

The raw material was weighed as much as 200 grams

and tested for water content and the calculation of the

need for cooking liquor. The raw material and

cooking liquor were put into the digester and the

operating conditions were set at constant temperature

and time at 120 minutes and a temperature of 110

After the specified operating conditions were

reached, the pulp was removed from the digester and

washed. The washing process was carried out with

hot water and followed by cold water until the

washing water is clean. The pulp obtained is analyzed

for ash, cellulose, Kappa number and yield.

4 RESULTS AND DISCUSSION

4.1 Effect of the Ratio of Cooking

Solution on Alpha, Beta and

Gamma Cellulose Content of Pulp

Figure 2: Cellulose Content (Alpha, Beta and Gamma) to

the Cooking Liquor Ratios at a Temperature of 110

C and

Cooking Time of 2 Hours

From Figure 2 above, it can be observed that alpha

cellulose content has increased with increasing

cooking liquor ratio. In the ratio of cooking liquor to

raw material of 1: 1, 2: 1, 3: 1, and 4: 1 the alpha

cellulose content had an increase of 76.22%, 79.32%,

81.32% and 83.11% respectively. The levels of beta

cellulose decreased by 16.34%, 14.21%, 12.22% and

10.21%, respectively, and for gamma cellulose

content was constant at 7.44%, 6.47%, 6.57%, and

6.68%.

An increase in the ratio of the cooking solution

increased the amount of lignin dissolved, thereby

increasing the cellulose percentage. In this case is an

increase in alpha cellulose, increasing the amount of

alpha cellulose will make the pulp quality better,

according to SNI 7274 and the Center of Pulp (SNI,

2008), good pulp quality standards with a minimum

amount of alpha cellulose 40%. In this research, on

all cooking liquor ratios produce higher amounts of

cellulose than 40%.

4.2 Effect of the Ratio of Cooking

Liquid to Ash Content of Pulp

Figure 3: Ash Content of Pulp to the Ratio of Cooking

Liquor at Temperature of 110

C and Cooking Time of 2

Hours

From Figure 3 it is shown that the higher the ratio of

cooking liquor to raw materials, the ash content will

decrease. At the ratio of 1: 1, 2:1, 3:1, and 4:1, the ash

content was 2.4%, 1.3%, 0.98% and 0.78%

respectively. The decrease in ash content is caused by

the dissolution of organic substances by the cooking

liquor. The more the cooking liquor is used, the more

organic matter can be dissolved.

According to SNI 7274 and the Center of Pulp

(SNI, 2008), a good pulp quality standard has 3%

maximum amount of ash.In this research, the pulp

was obtained with ash content at various variations

lower than 3%. This shows that the pulp produced

were in accordance to the standard and has good

quality.

100

1:1 2:1 3:1 4:1

Cellulose Content (%)

Cooking Liquor Ratio

Alpha Selulosa

Beta Selulosa

Gamma Selulosa

1:1 2:1 3:1 4:1

Ash Content (%)

Cooking Liquor Ratio

Effect of Cooking Liquor Ratio on Lignin Reduction in Pulping Process from Cogongrass and Lemongrassleaves using Soda Process

381

4.3 Effect of the Ratio of Cooking

Liquor on Kappa Numbers

Figure 4: Pulp Kappa Number on the Ratio of Cooking

Liquor at 110 °C and 2 hours Cooking time

From Figure 4 above it can be observed that the

Kappa number has decreased along with the increase

in the cooking liquor ratio. The Kappa number is the

required number of milliliters of potassium

permanganate (KMnO

) required or absorbed by 1

gram of dry pulp under standard conditions [11]. The

purpose of Kappa number analysis is to determine the

effectiveness of the delignification process, where the

Kappa number shows the remaining lignin content of

the pulp.

At the ratio of 1:1, 2:1, 3:1, and 4:1, the Kappa

number is 21.41, 18.27, 16.17, and 13.17

respectively. An increase in the ratio of the cooking

liquor increased the amount of lignin dissolved. The

greater the dissolved lignin, the lower the Kappa

number, which shows the better quality of the pulp

with a low lignin content.

4.4 Effect of the Ratio of Cooking

Liquor to Pulp Yield

Figure 5: Yield of Pulp on Ratio of Cooking Liquorat 110

°C and Cooking Time of 2 hours

From Figure 5 above shows that at the ratio of 1:1,

2:1, 3:1, and 4:1,the yield obtained were 68.23%,

78.33%, 62.21% and 56,31% respectively. Yield has

increased from a ratio of 1: 1, to a ratio of 2: 1, this

increase is because at the ratio of 1:1 less cooking

liquor are used so that the pulping process was less

effective, and it caused a decrease in the yield. In the

ratio of 2:1 to 3:1 the yield decreased, and also for the

ratio of 4:1, which were caused by the dissolution of

cellulose (degraded cellulose) in the cooking process.

5 CONCLUSION

1. The lowest ash content is at a ratio of 4:1 of

0.78%.

2. The highest alpha cellulose content isat a ratio of

4: 1 of 83.11%.

3. The lowest Kappa number is at a ratio of 4:1 of

13.17.

4. The highest pulp yield at a ratio of 2:1 is 78.33%.

5. In applications that require high levels of alpha

cellulose, and lignin as low as possible, it can be

done with a ratio of 4:1 cooking liquor, but if the

high yield is required, the comparison of cooking

solution 2: 1 can be used.

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