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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.