UNIVERSITI PUTRA MALAYSIA

ORGANOSOLV PULPING OF PARASERIANTHES FALCATARIA

LAURA L. BUNYE

FH 1990 2

EXAMINATION OF PROJECT REPORT

NAME OF CANDIDATE LAURA L . BUNYE

, TITLE OF PROJECT ORGANOSOLV PULPING OF

PABASERIANTHES FALCATARIA

APPROVED BY :

1-V.3���� ...... . D��\JOSE V. ZERRUDO

n)1l \ tt( 0

(MAJOR SUPERVISOR/EXAMINER)

t � .... �.. . .............. . . . � ,

HR • PARIDAH HOHD TAHIR ( MIN R SUPERVISOR/EXAMINER)

.. ��.��: .. � ..... . PROF . HADYA DR�ZALI ABDUL KADER

( CHAIRMAN, DEPT. OF WOOD SCIENCE) AND TECHNOLOGY

-.:..:.=�:-:-�� ........... . IS B . AWANG

FORESTRY)

NOVEMBER, 1990

ORGANOSOLV PULPING

OF PARASERIANTHES FALCATARIA

by

LAURA L . BUNYE

This report i s submitted in partial ful fil lment of the requirements for the

degree of Masters of Science (Wood Industries Technol ogy )

Faculty of Forestry universiti Pertanian Malaysia

Serdang, Selangor Malaysia

NOVEMBER , 1990

ABSTRACT

The potential of organosolv pulping using Paraserianthes falcataria as a raw material was studied. organosolv pulping was carried out under 2 conditions of catalyst addition - 75% ethanol plus 0 . 05 M CaCI2; and 75 % ethanol plus 0 . 10 M CaCI2; and without catalyst - 75 % ethanol only.

The results indicated that without catalyst, organosolv pUlping was incapable of reducing cooking chips into pulp. Catalyzed organosolv pulping at 0 . 0 5 M CaCl2 produced pulp with screened yield of 45 . 31 % and 46 . 67 % for the 0.10 M CaCl2 condition. These yields were slightly lower than the 48 . 56 % of kraft. The brightness of the unbleached pulps were 16 . 8 % and 15 . 9 % for organosolv pulping with 0 . 05 M and 0 . 10 M CaCl2 conditions, respectively. These pulps were generally darker than the kraft pulp which had a brightness of 31 . 6 % . The strength properties i. e. , burst, tear, tensile, stretch, and folding endurance of the two catalyzed organosolv pulps were very low compared to that of kraft pulp control. The total solids recovered from the black liquor of uncatalyzed organosolv process was 4. 72 % while the catalyzed organosolv pulping were 7. 0 % for 0 . 0 5 M caCl2 condition and 7 .1 % for 0 . 10M caCl2 condition.

ii

ACKNOWLEDGEMENT

Glory, honor and praise to God Almighty and savior

and Lord Jesus Christ for sufficient providence that led

to the completion of this project.

A warm gratitude to Dr. Jose V. Zerrudo and Mrs.

Paridah Mohd. Tahir for their supervision, comments and

guidance.

Appreciation for the Faculty's Laboratory staff;

Forest Research Institute of Malaysia's Pulp and Paper

division staff; and to special friends, in particular

Mr. Pipin Permadi for their plentiful contributions and

helps.

Sincere gratitude is highly due to Asean Timber

Technology Centre for the scholarship grant and project

financial support. Also, a heartiest appreciation to

the management of Canlubang Pulp Manufacturing

Coorporation for giving the official study leave.

Finally, showers of love and blessings be on my

beloved father, late mother, brothers and sisters for

providing the much needed encouragement and prayers for

the accomplishment of this study.

iii

TABLE OF CONTENTS

PAGE Title page . . . . . • . • • • . . . . . . . . . . . . . . . . • . . . . • . . . • . . i Abstract . . . . • . . . . . . . . . • . . • . . . . . . . . . . . . . . . . . . . . . . . . • i i �c:l1()ViJL�Cl��]QEaIl1: • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • iii Table List List List

of of of Of

Contents Tables Figures Plates

iv vi

vii viii

INTRODUCTION 1

Objectives 2

LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . 3

Ethanolysis Reactions Of Lignin . . . • • . • . • • . . . . . 3 Organosol v Pulping . . . . . . • . . . . . . . . . . . . . . • . • • . • • 4 The Organosolv Processes . . . . . . . . . . . . . . • . . • . • . . 6

Kleinert Organosolv Process . . . . . . . . . . . . • • . 6 ALCELL Organosolv Process . . . . . . . . . . . 8 MD Organocell Process . . . . . . . . . . . . . . • • • • . . . 11

Mechanisms Involved In Organosolv Processes. . . . 1 3 Kleinert Uncatalyzed Process . • . . . . . . . . . . . . 13 Neutral Alkali Earth Metal ( NAEM)

Catalyzed Solvent Pulping . . . . . . . . • . . . • 15

Advantages And Disadvantages Of Organosolv Processes .............................. 17

Commercial Applications Of Organosolv Processes. 18 Wood Species For Organosolv Processes • • • . • . . • • . 19 Organosolv Pulp Properties . . . . . . . . . . • . . . . . . . . . . 20 Description of Paraserianthes falcataria ....... 2 1

Morphological Characteristics . . . . . • . . • . • . . 2 1 Chemical Composition . • . . . . . . • . . . • • • . . . . . • 2 2

Kraft Process And Pulp And Paper Properties Of Paraserianthes falcataria . . . . . . . . . • • • • . 2 3

iv

MATERIALS AND METHODS 2 4

Raw Material Preparation . . . . . . . . . . . . . . . . . . . . . 2 4 Organosolv Pulping . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 6 Handsheet Making . . • • • . . . . . . . . . . . . . . . . . . . . . . . . 2 9 Testing For Pulp strength . . • . • . . • . • . • . • • • • . • • 30 Black Liquor Total Solids . . . • • • . • • • • . . . • • . • • • 31 Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

RESULTS AND DISCUSSIONS • • • • • • • • • • • • • • • • • • • • • • • • • • • 34

Raw Material Preparation . . . • . . . . . . . . . . . . . . . . • 34 Organosolv PUlping . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Testing For Pulp Strengths . . . . . . . . . . . . . . • . . • . 40 Black Liquor Total Solids . . . . . . . . . . . . . . . . . • . . 56

CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

RECOMMENDATIONS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 59

REFERENCE S . . • • . . . . . • • • . • • • • • . . . . . . • . . . . . . . • • • • . . • • 60

v

TABLE

1

2

3

4

5

6

7

8

9

10

LIST OF TABLES

TITLE

Fiber Morphology Of Paraserianthes falcataria

Chemical Composition Of Paraserianthes falcataria

preliminary organosolv Pulping Of Paraserianthes falcataria

PUlping Conditions Adopted For Experiment

standard Procedures For Paper Testing

Results Of The Preliminary Organosolv pulping Of

Paraserianthes falcataria

Pulping Properties Of Paraseriathes falcataria

Pulps strength properties Of Paraseriathes falcataria From Organosolv And Kraft Processes

Pulps strength properties Of Paraserianthes falcataria At Freeness Of 350 CSF

Total Solids Recovered From The Black Liquor Of Organosolv Processes

vi

PAGE

2 2

2 2

2 6

2 8

31

35

36

41

54

56 '

FIGURE

1

2

3

4

5

6

7

8

9

10

11

LIST OF FIGURES

TITLE

simplified Flowsheet Or Kleinert Organosolv Process

Flow Chart Of ALCELL Organosolv Process

Flowsheet Of MD organocell Process

cation Adsorption Onto Cellulose , And Proton Generation During NAEM Catalyzed Organosolv Pulping

cutting Pattern Of Handsheets Into Testing samples

Freeness vs Beating Time Organosolv And Kraft Pulps

Of

The Burst Index Of Catalyzed Organosolv And Kraft Pulps

The Tear Organosolv

Index Of Catalyzed And Kraft Pulps

The Tensile Index Of Catalyzed Organosolv And Kraft Pulps

The Stretch Of Organosolv And

Catalyzed Kraft Pulps

The Folding Endurance Of Catalyzed Organosolv and Kraft Pulps

vii

PAGE

7

9

12

16

32

42

49

50

51

52

53

PLATE

1

2

3

4

5

6

7

8

9

10

11

LIST OF PLATES

TITLE

Paraserianthes falcataria Plantation In Kemasul, Malaysia

Billets of Paraserianthes falcataria

Paraseriathes falcataria Air Dried Chips

Tree Pahang,

MK Digester Used In pulping

Rotavapor Used In Ethanol Recovery

Unsoftened Paraserianthes falcataria Chips From Uncatalyzed Organosolv Pulping

Pulp Of falcataria Organosolv Addition

Paraserianthes From Catalyzed

with 0.05 M CaCl2

Pulp Of Paraserianthes falcataria From Catalyzed Organosolv with 0 . 10 M CaCl2 Addition

Handsheet From Catalyzed Organosolv Process with 0.05 M CaCl2

Handsheet From Catalyzed Organosolv Process with 0.10 M CaCl2 Addition

Black Liquor And Total Solids Of The Organosolv Processes

viii

PAGE

25

25

27

27

3 3

3 8

3 9

3 9

43

44

57

INTRODUCTION

The chemical pulping processes in use today have evolved

over the years and generally speaking have satisfactorily

fulfilled the needs of paper and paperboard manufactures.

Nevertheless, there

different pulping

is a growing interest in radically

methods that are based on the use of

as pulping agents. These methods are

"organosolv" pulping processes (Aziz and

organic solvents

referred to as

Sarkanen, 1989) .

Organosolv processes are techniques which use organic

solvents to separate lignin and the carbohydrate portions o f

the wood. Lately, organosolv pulping has been generating

headlines (Pulp and Paper Canada,

industrial processes have been patented.

In 1985, a session of pulping

1984) and

conference

several

held in

Atlanta was devoted to this subject and the topic was also

discussed in recent seminars conducted in Hamburg, Federal

Republic of Germany and Appleton, Wisconsin. The developments

in the field of alcohol pulping were presented at the

Appleton seminar.

Organosolv pulping is based on the use

solvents such as methanol, ethanol and higher

pulping liquor. Basically, this is different

of organic

alcohols as

from the

conventional processes because it does not make

sulphur containing chemicals that causes emissions

use of

of foul

2

odors. It is claimed to be pollution-free. Moreover,

alcohol, as well as other pUlping by-products such as,

lignin, sugars and volatile components can be recovered

easily (Williamson, 1987) . This means cost savings,

additional income and less hazards for both people and

environment.

Indeed, some organosolv processes are reaching the stage

of realistic industrial applications as auxiliary methods for

adding incremental hardwood capacity to the existing pulp

mills ( Aziz, 1989) . Eventually, large scale production units

may evolve for pUlping uniform raw materials from fast

growing plantation species. No study has been carried out on

the pulping of tropical hardwoods or fast growing plantation

species by this process, as far as can be determined.

OBJECTIVES

The specific objectives of this study are the following :

1 ) to evaluate

processes on

the potential of organosolv

Paraserianthes falcataria (batai)

different pUlping conditions

pulping

at 3

2) to analyze the black liquor for recoverable total

solids; and

3 ) to evaluate the strength properties of batai organosolv

pulps.

3

LITERATURE REVIEW

Ethanolysis Reactions Of Lignin

The prolonged heating of lignified materials with

ethanol or some other alcohol plus hydrochloric acid results

in "ethanolysis" or "alcoholysis" reaction of lignin

(Schubert, 1965) .

Brauns ( 1952) noted that during the alcoholysis of

lignin, three reactions may take place simultaneously namely,

(a) condensation of part of the lignin with the alcohol,

resulting in a soluble "alcohol Lignin, " (b) condensation of

part of lignin with itself resulting in a product of lesser

reactivity, and (c) an "alcoholytic cleavage" of part of the

lignin resulting in its depolymerization to smaller lignin

building units which may be followed by the condensation of

some of these units with the reacting alcohol.

In recent years, alcoholysis and especially ethanolysis,

has found use as an important analytical tool in helping to

establish whether an isolated product is really derived from

lignin. Thus, on treating "protolignin" with absolute alcohol

in the presence of catalytic amounts of hydrochloric acid,

Hibbert and his co-workers ( obtained a series of

monomeric phenylpropane derivatives. The reaction is now

often used as a "test" for lignin preparations. Kratzl and

Klein ( have applied the reactions to charactererize

and identify certain lignin preparations.

4

Orqanosolv pulpinq

Organosolv pulping process is the technique which uses

organic solvents to separate the lignin from the carbohydrate

portion of the wood.

Organosolv pulping has been classified into

1) uncatalyzed process, and

2) catalyzed process, which is further subdivided into

a) acid catalyzed, and

b) alkaline catalyzed.

Pazner and Cho ( 1989) divided solvent pulping into two

categories, namely : uncatalyzed and catalyzed processes. The

catalyzed process was further subdivided by Aziz and Sarkanen

( 1989) into acid and alkaline catalyzed processes.

The uncatalyzed process is done without any catalyst.

Aranovsky and Gortner ( 1936) found that primary alcohols

are more selective delignifying agents than secondary or

tertiary alcohols. Recently, it has been suggested that

monovalent and polyvalent alcohols have higher pulping

efficiencies in the presence of water, although anhydrous

alcohols have been found to be more selective delignifying

agents than their aqueous counterparts.

The

or acid

recommend

Orth ( US

chloride

solvents

indicated

propionic,

suitable

patented

5

catalyzed process uses small amounts of alkali

as catalysts. Kleinert and Tayenthal (1932)

a broad range of acid reacting salts. Orth and

Patent 4, 017, 64 2) patented the use of aluminum

(AICI3. 6H20) as the prefered catalyst for

of aqueous glycol or glycol ether. They further

that organic acids such as formic, acetic,

oxalic, malic, citric

catalysts. Pazner and

or pthalic

Chang ( US

acids are

patent, 1983)

sodium hydroxide, ammonium sulphide, sulphite

anthraquinone,

alkali earth

anthraquinone ammonium sulphide and neutral

metals ( NAEM) such as calcium chloride and

magnesium chloride, as suitable catalysts for organosolv

pUlping.

Organic solvents with pH values lower than 4. 75 are also

used and it has been shown that such organic acids are better

than mineral acids for the pUlping of softwoods. None of

these catalysts,

expectations of

viscosity at low

1989) . Pazner has

metals, (calcium

however, has satisfied the general

producing pulps of high strength and

residual kappa number (Pazner and Cho,

patented

chloride

the

and

salts of

magnesium

alkaline earth

chloride) as

catalysts in organosolv liquors with high methanol and

ethanol contents (Canadian Patent, 1981) .

6

Acid catalyzed processes are often operated

without an acid catalyst, since the acetic acid released from

the wood during pulping provides the alcohol with the needed

acidity. In such cases, the temperature of reaction is in the

range of l8 5-2l0oC. Acid catalyst may be used to lower

reactor temperature and pressure. On the other hand,

alkaline organosolv processes commonly make use of NaOH or

Na2So3. The role of organic solvents is simply to promote

the dissolution of lignin.

The organosolv Processes

There are 3 existing recognized organosolv pulping

processes (Aziz and Sarkanen, 1989) namely, (1) Kleinert

(2) ALCELL and (3) MD .

Kleinert organosolv Process

Figure 1 shows a simplified description of the process.

Pulping occurs in a counter current reactor. The

pulping temperature is approximately 1950C. Pre-steamed chips

enter at the top of the reactor, while the pulping liquor

without any catalyst, pre-heated to 100 - llOoC, enters at

the bottom. The liquor flows upward, extracting dissolved

materials from the chips.

The spent liquor leaves the digester through a strainer

ring located at the top of the digester and enters a

quintuple evaporator. The combined condensates from the

evaporator are collected for alcohol recovery. The heavier,

viscous lignin phase flows into a separation tank and is

I I I I I I I I I I I I I I I I I I

Heal: E;{cnanger

Preneal:eo Soivenl:

Feeo val ve

Separal:IOn Feeo valve Tank

Pul pIng

Screw Press

QUlnl:upl e Evaporal:or

L i gnin

Conoensal:es to alconol recovery

fULP

To alconoi F-.ecovery

Screw Press

Aqueous i'llaUH 3-0 gil,

_ _ 0_ IVV L

FIgure 1. Flowsneel: For t ielnerl: Cirganosoiv 5ysl:em

7

Aqueous Sugar Solution

8

collected from the tank bottom while an aqueous solution of

hemicellulose sugars is taken off from the top.

The pulp is withdrawn from the bottom of the digester

through a screw press which removes part of the organosolv

liquor. The rest of the liquor is recovered from a pulp

washer using aqueous NaOH as wash water. A second screw

press completes the washing operation.

This process has two important limitations which are

frequently overlooked. First, the production of bleachable

grade pulps from softwoods proceeds smoothly to kappa number

of 8 5 to 100 but comes to a virtual standstill at this point.

The strength properties of these pulps are satisfactory, but,

can hardly be expected to successfully compete with

conventional kraft process in the manufacture of linerboard

and bagpulps. The second limitation is in the pulping

properties of hardwood species which are somewhat variable.

These characteristics can cause problems and in the worst

case, require segregation of species in the wood yard.

ALCELL organosolv Process

This process evolved and was developed by Repap

Technologies out of the ideas and studies made by Katzen et.

al. ( 1981) to refine and improve the application of

organosolv pulping in batch systems. Their idea was to apply

the principle of gradual displacement of the pulping liquor

in the digester with hot organosolv wash liquors. The process

flow chart is shown in Figure 2.

.. ,..

u

I

G

E

5

T

E

R

Pul p

Grl1:

9

.. ., Secona ana 1:nl ra s1:age 11 quor 1:0 ne:'�1: S1:age

FIrS1: s1:age spen1: lIquor 1:0 recovery

LIgnIn freClpl1:a-

1:10n

LI,;,nIn wasnlng

fn S1: III a1: Ion t--•• al conol Tower "OIl s

.. LIgnIn

t--...... -r •. Th 1 c K-enlng

LIgnIn drYIng and bagging

Vacuum � �ugar � ____________ .. " Evaporator ::;,yrup, � 50 k Solids

ana ScreenIng Pul p Three Pulp i<n01: r-t ana H S1:orage � S1:age -f uryin g

removal Cl eanIng Bleaching and Balin g

.� 1iII ....... -------Llquor Trom secona ana �lrS1: stage use

.... Fresn l Iquor �rom 1:nlra s1:age

Flgure �. Flowsnee1: For HLL�LL �u l p l ng frocess And SUDsequen1: �ecovery Of By Produc1: Chemicals

I I I I I I I I I I I I I I ,

10

Preheated chips ( 800C) are packed in the digester using

steam. The purpose of steaming is to displace air from the

chips. Preheated solvent that has been previously used as a

wash liquor from two earlier batches is pumped into the

digester and the temperature rapidly raised to between 1900 C

and 2100C, corresponding to an operational pressure of 500

psi. The liquor is circulated continuously in the digester

during the pUlping period. At the end of this period, the

liquor in the digester is displaced by wash liquor that was

used in the second washing stage of the previous batch. The

displaced liquor from the digester flows to the lignin and

sugar recovery system. The third stage wash liquor is

displaced by fresh liquor and flows into an intermediate

storage tank for use in the second stage. The second stage

wash liquor is drained into another storage tank for use in

the digester.

At this point, the digester contains soaked, delignified

chips and alcohol water vapor at pulping temperature and

pressure. The pressure is released and the vapor is

condensed for reuse as fresh pUlping liquor. Finally, the

alcohol remaining in the digester is driven off by steaming •

The pulp is diluted with water and pumped out of the

digester for cleaning and bleaching treatments. The first

stage spent liquor entering the by-product recovery system

is first splashed and then diluted with process water to

precipitate the dissolved lignin. After settling, the solid

lignin is separated by centrifugation, washed and dried.

1 1

The filtrate enters a distillation tower, where alcohols and

some acetic acid and furfural are recovered. Finally, the

remaining aqueous liquor is further evaporated to a sugar

syrup.

MD organocell Process

This process is a modification of the Kleinert

process for the purpose of producing bleachable grade pulps

from softwoods. The system is shown

Softwood chips are impregnated with

in Figure 3.

methanol-water

before entering the first stage continuous reactor. The first

stage is operated under a 40 bar pressure at 1950C.

Approximately 20 % of the lignin and a major part of the

hemicellulose is removed from the chips.

The chips are then transported to the second stage

digester, which is operated at 1700C under alkaline

conditions. The combined residence time in both reactors is

only 4 5 minutes. The strength properties of the pulp produced

are only slightly lower than those of corresponding kraft

pulps. Organics and NaOH are recovered from the second stage

liquor. After the methanol is recovered, the remaining

liquor enters an electrolytic cell which separates NaOH and

precipitates lignin in a filterable form.

Soft.wood Chips t ...... ----------- i'ieOH-H20 Impregnat.ion

hydraul ic t.ransport.

first. st.age -

second s1:age _ _ _ 0_

-+0 bar r ___ 0_

�'-IV L� �/v L

"j� ... IL

I i'ieOH-H20 I i.,jaOH in

i'ieOH-H2O

... , �, L J Evaporat.ion Evaporat.10n I _i- I i'ieOH

Recovery � ,.

El ect.rol yt.ic

� Separat.ion

i.,jaOH Recovery

� , .. ,. Lignin Li I�n i n

Recovery � Fil t.rat.ion

Lignin Filt.rat.ion

� ,. �, Evaporat.ion L I Evaporat.ion I J, I

Hemicel l ul ose Recovery

Figure ..::.. Flowshee� of nu Organocel l Pul ping Syst.em

... ..

12

Pulp

Washing

I I I I I I I I I ( I I I I I I

13

Mechanisms Involved In organosolv Processes

Pazner and Cho (1989) stated that the mechanisms

involved in solvent pulping have not been investigated in

detail, and that opinions as to the selectivity of solvents

during delignification vary greatly.

Aranovsky and Gortner (1936) suggested that the pulping

efficiency of solvents is related to the zeta potential of

the cellulose solvent interface. On the other hand, Kleinert

(1975) suggests that lignin depolymerization is a free

radical process and that solubilization depends on pH,

temperature or solvent concentration. Kleinert recommended

the use of systems with near neutral pH since low pH values

are also responsible for the hydrolysis of hemicellulose.

Kleinert Uncatalyzed Process

A detailed analysis of Kleinert process was undertaken

by Baumeister and Edel (1980) giving particularly close

attention to the conditions of solvent composition,

isothermal heating and liquor flow. They concluded that the

rate and degree of delignification are controlled by opposing

mechanisms, i. e. , hydrolysis of the lignin macrogel and

condensation of the solvolysis products, respectively. Both

of these reactions are catalyzed by protons, which are

modified by the alcohol concentration in the liquor.

Evidently, lignin dissolution is considerably retarded at

alcohol concentrations greater than 50%.

14

There is a high initial topochemical effect resulting in

the formation of fissures, caused by partial delignification

in the middle lamella. Fiber liberation, however, does not

occur until a later stage of the cooking. High

temperature cooking leads to a rapid increase in the acids

concentration of the hemicellulose rich regions ( P, Sl, S2)

of the cell wall and causes in situ condensation and

precipitation of the solvolysis lignin products. The

of the condensed lignin from the cell wall

removal

is not

possible until sUbstantial amounts of the hemicelluloses are

solubilized and the cell wall is opened up through the

creation of macropores. As such, long cooking times could

lead to rapid degradation of the cellulose, resulting in low

viscosity.

with open structured hardwoods, cell wall accessibility

is a lesser problem. However, the combined effects of high

temperature, long cooking times and uncontrolled low pH could

result in dark pulps of unacceptably low viscosity and

unacceptably high (up to 10%) rejects content. Baumeister and

Edel ( 1980) concluded that the isothermal reaction conditions

( uncata1yzed 30 to 50% alcohol ) of the Kleinert process are

unsuitable for the production of paper grade pulp from most

woods except aspen and the poplars.

15

Neutral Alkal i Earth Metal ( NAEM) Cataly z ed Solvent pulping

The mechanisms of catalysis by neutral alkali earth

metal ( NAEM) salts in methanol pUlping has not yet been

investigated in detail (Pazner and Cho, 1989) . However, the

metal ion sequestering properties of wood and lignin have

been known for sometime. In all probability , the primary

step in the catalysis adsorption of divalent ions on the

wood is through the carboxylic acid groups ( Figure 4). This

causes a rapid drop of pH in the pUlping liquor even before

cooking commences. The divalent ions apparently stabilizes

the carboxylic acid groups of carbohydrates while reducing

the extent of acetic acid formation upon high temperature

splitting of O-acetyl moieties from the hemicellulose. The

formation of Ca-2 and Mg-2 acetates by reactions of the

catalyst with the liberated acetic acid contributes 'further

to the excellent pH control in the NAEM catalyzed solvent

system.

The solvent effect of the NAEM ion catalyses is to

protect the cellulose from hydrolytic degradation and to

arrest the deacetylation of the hemicellulose by preventing

the excessive drop in cooking liquor pH.