CATALYTIC SELECTIVITY IN ALCOHOL ORGANOSOLV - cIRcle

236 Pages·2009·10.74 MB·English

CATALYTIC SELECTIVITY IN ALCOHOL ORGANOSOLV PULPING
OF SPRUCE WOOD
By
DOMTNGGUS YAWALATA
In, Pattimura University, Ambon - Indonesia, 1987
M.Sc., The University of British Columbia, 1996
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
in
THE FACULTY OF GRADUATE STUDIES
(Faculty of Forestry)
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
February 2001
© Dominggus Yawalata, 2001
In presenting this thesis in partial fulfilment of the requirements for an advanced
degree at the University of British Columbia, I agree that the Library shall make it
freely available for reference and study. I further agree that permission for extensive
copying of this thesis for scholarly purposes may be granted by the head of my
department or by his or her representatives. It is understood that copying or
publication of this thesis for financial gain shall not be allowed without my written
permission.
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Department of
The University of British Columbia
Vancouver, Canada
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ABSTRACT
Development of a more efficient and environmentally friendly pulping process is
seen as a necessity to cope with problems currently faced by pulp and paper industries.
The organosolv pulping process seems to be the right choice to deal with the problems.
Although many organosolv pulping process variants have been developed and are at
various stages of commercialization, most processes are incapable or struggle with pulping
softwoods. Furthermore, employment of a catalyst in organosolv pulping liquor appears
to be essential for softwood pulping. However, systematic studies of catalyst
effectiveness, especially for softwood pulping by organosolv means, are lacking.
Therefore, the objectives of this research were to investigate the effect of catalysts on
pulping behavior, selectivity, pectin removal and delignification leading to fiber separation
in a catalysed alcohol organosolv pulping process.
Under the specified pulping conditions, it was found that not all catalysts used in
the organosolv pulping of softwood were able to liberate the fibers. The pulping
outcomes were different, depending on the catalyst species. Different species of cations
and anions had an impact on cooking liquor pH that subsequently controlled the pulping
process and its outcomes. Generally, the pH of the cooking liquor controlled the pulping
selectivity and fiber separation. Furthermore, pulping selectivity and topochemistry, and
not necessarily delignification alone, control both fiber liberation and fiber quality. For
high fiber yield and quality, control of the final pH between 3.8 and 4.2 is a necessity. In
some cases, the use of two different catalysts in the cooking liquor showed a synergistic
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effect on the improvement of fiber liberation.
It is concluded that neither mono- nor trivalent acidic inorganic salts, nor simple
organic acids in themselves, except citric acid, can be used as catalysts for effective fiber
liberation in organosolv pulping, due largely to the uncontrolled drop of pH below 3.5, at
which point delignification becomes significantly retarded. The mystery of the unique
neutral alkali earth metal (NAEM) salt catalyst effectiveness is now fully explained and
described. Investigation of NAEM catalysed pulps showed total loss of arabinose and
galactose from among the carbohydrates of the pulp as if their presence controlled the
process of fiber liberation.
Early fiber liberation resulting in high pulp yield and viscosity can only be
accomplished with a cooking liquor possessing high chemical and topochemical selectivity
for lignin. In this respect, effective removal of the middle lamella compounds is seen as
the key factor for fiber liberation. On the other hand, the removal of middle lamella
compounds is found to be an antagonistic process, in which the removal of esterified
pectin preferred less acidic pH due to the P-elimination mechanism while more acidic
cooking liquor (pH <4.5) was required to enhance and accelerate delignification. At low
pH (<3.8), however, carbohydrate degradation and removal are also enhanced due to
hydrolysis. The enhancement of carbohydrate degradation and loss grows with increasing
cooking liquor acidity, while delignification decreases or even stops. The removal of
middle lamella compounds, to liberate the fibers, basically followed 2 different pathways:
1) the removal of pectin and some hemicelluloses, followed by delignification, as in the
neutral alkali earth metal salt catalysed process, and 2) the removal of hemicelluloses,
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followed by delignification and pectin removal, as in the citric acid catalysis. It was also
found that in all organosolv cooks, fibers can not be completely separated without
removing all arabinose and galactose.
Extending the cooking beyond the fiber liberation point provides no benefit at all,
because the extent of additional delignification is small and is attained at the expense of
carbohydrate degradation and loss, and lignin re-precipitation. Therefore, highest yield is
obtained if delignification is halted at the fiber liberation point. Unexpectedly, the
effectiveness of citric acid as a catalyst was found to be comparable to that of the NAEM
salt catalysed organosolv pulping process. In both NAEM salt and citric acid catalysed
organosolv pulping with 80 % methanol, the loss of hemicelluloses comprising xylose and
mannose increased when the degree of delignification exceeded 60 %.
The mechanism of fiber liberation in the NAEM salt catalysed organosolv pulping
process can now be described as "versatile" being able to affect both initial removal of the
pectin and hemicelluloses (arabinogalactan) followed by bulk and residual delignification.
NAEM salt catalysts therefore play a double role : 1) effectively promote the initial pectin
removal at pH >5, and 2) effectively buffer the cooking liquor against uncontrolled pH
drops as more and more protons are liberated due to ion exchange with carboxyls and
liberation of acetyls. The role of pectin dissolution in controlling effective fiber liberation
in organosolv pulping of softwood is described for the first time. The topochemistry of
pectin removal from spruce wood was followed by immunolabelling followed by
fluorescent microscopy of thin cross-sections.
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TABLE OF CONTENTS
ABSTRACT ii
TABLE OF CONTENTS v
LIST OF TABLES viii
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xv
ACKNOWLEDGEMENT xvi
1. INTRODUCTION 1
1.1. Background 1
1.2. Objectives 4
1.3. Hypotheses. 5
1.4. Outline of Experiment 6
2. LITERATURE REVIEW 9
2.1. Chemical Constituents of Wood 9
2.1.1. Lignin 10
2.1.2. Cellulose 12
2.1.3. Hemicelluloses 13
2.1.4. Extractives 14
2.1.5. Pectic substances 16
2.1.6. Distribution of the main chemical constituents in the cell wall... 18
2.1.7. Carboxyl group in wood 19
2.2. Strength of Acidic Protons 24
2.3. Organosolv Pulping 26
2.3.1. Alcohol-based solvent pulping . . 27
2.3.1.1. Acidic alcohol-based solvent pulping 27
2.3.1.1.1. ALCELL process 32
2.3.1.1.2. NAEM process 36
2.3.1.2. Alkaline alcohol-based solvent pulping 39
2.3.1.2.1. ASAM process 40
2.3.1.2.2. ORGANOCELL™ process 43
2.3.2. Organic acid and ester pulping 46
2.3.3. Other solvent pulping processes 50
v
2.4. Factors Affecting Delignification 51
2.4.1. Effect of type of lignin and linkages 51
2.4.2. Effect of solvent 54
2.4.3. Proton catalysis 56
2.5. Topochemistry of Delignification 61
2.6. Pectin Degradation and Dissolution 64
3. MATERIALS AND METHODS 67
3.1. Raw Material 67
3.2. Methods 67
3.2.1. Pulping 67
3.2.1.1. Kraft pulping 67
3.2.1.2. Organosolv pulping 69
3.2.1.2.1. Pulping conditions and procedures 69
3.2.1.2.2. Pulp washing 70
3.2.1.2.3. Pulp screening 70
3.2.2. Chemical analyses on the raw material and/or pulp 70
3.2.2.1. Extractives 70
3.2.2.2. Klason lignin (acid-insoluble lignin) 72
3.2.2.3. Acid-soluble lignin 73
3.2.2.4. Sugar analysis 74
3.2.2.4.1. Sample preparation 74
3.2.2.4.2. HPLC analysis 74
3.2.2.4.3. Establishment of the standard curve 75
3.2.2.4.4. Quantification of sugars 76
3.2.2.5. Holocellulose 76
3.2.2.6. Alpha-cellulose 77
3.2.2.7. Kappa number 78
3.2.2.8. Viscosity 79
3.2.3. Acidity and buffer capability of cooking liquor 79
3.2.4. Immunocytochemical labelling of pectin for fluorescent
microscopy 81
3.2.4.1. Sample preparation and fixation 81
3.2.4.2. Dehydration, embedding and sectioning 82
3.2.4.3. Protocol of immunolabelling 82
3.2.4.4. Visualization of slides with a fluorescent microscope . .83
4. RESULTS 85
4.1. Chemical Composition of Spruce Wood 85
4.2. Pulp Yield 86
4.3. Residual Lignin and Viscosity of the Pulp 96
4.4. Monitoring the pH of Cooking Liquor 105
4.5. Sugar Analysis Ill
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4.6. Delignification and Carbohydrate Removal 118
4.7. Immunocytochemical Study 133
5. DISCUSSION 146
5.1. Effect of Catalysts on Pulp Production Capability in Organosolv
Pulping 146
5.1.1. Uncatalysed organosolv pulping 147
5.1.2. Catalysed organosolv pulping 148
5.1.2.1. Organosolv pulping with inorganic acid catalysts . . .149
5.1.2.2. Organosolv pulping with organic acid catalysts . . . .150
5.1.2.3. Organosolv pulping with monovalent metal ion
catalysts 151
5.1.2.4. Organosolv pulping with divalent metal ion
catalysts 152
5.1.2.5. Organosolv pulping with trivalent metal ion
catalysts 154
5.1.2.6. Organosolv pulping with Mg-salt of different
anion species catalysts ....155
5.1.2.7. Organosolv pulping with combination catalysts . . . . 155
5.2. Effect of Extended Cooking 157
5.3. Effect of Cooking Liquor Acidity 159
5.4. Pulping Selectivity 162
5.5. Behavior of Delignification 165
5.6. Carbohydrate Degradation and Removal 169
5.7. The Role of Pectin in Fiber Liberation 172
5.7.1. Removal of pectins 175
5.7.2. Mechanism of pectin removal in organosolv pulping 178
5.8. Mechanism of Middle Lamella Removal in Organosolv Pulping 180
5.9. Fiber Liberation : An Antagonistic Process 181
5.10. Mechanism of Fiber Liberation in the NAEM Process 184
6. CONCLUSIONS AND FUTURE RESEARCH . . . 187
6.1. Conclusions 187
6.2. Reasons for Lower Strength of Organosolv Pulp :
A Suggestion for a Further Study 190
REFERENCES 193
APPENDICES 212
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LIST OF TABLES
1. Chemical composition of some wood species 10
2. Some common fatty acids 23
3. pKa values for some acids 25
4. Comparative paper strength properties of hardwood ALCELL and kraft
pulps at 300 mL CSF 35
5. Comparative paper strength properties of various types of unbleached pulps 38
6. Cooking conditions in the AS AM pulping process 41
7. Cooking conditions of the modified ORGANOCELL process 44
8. Three-stage MTLOX pulping conditions for hardwood and softwood, two-stage
pulping conditions for non-wood species, and properties of the pulps 49
9. Proportions of types of linkages connecting phenylpropane units in spruce
(Picea abies) and birch (Betula verrucosa) lignins (MWL) 53
10. Chemical composition of spruce wood 85
11. Sugar composition of spruce wood 85
12. Pulp yields and reject contents in organosolv pulping with and without
catalysts of chloride salts of monovalent cations 89
13. Pulp yields and reject contents in organosolv pulping with catalysts of
chloride salts of divalent cations 89
14. Pulp yields and reject contents in organosolv pulping with catalysts of
chloride salts of trivalent cations 90
15. Pulp yields and reject contents in organosolv pulping with Mg-salt catalysts 90
16. Pulp yields and reject contents in organosolv pulping with inorganic acid catalysts. .91
17. Pulp yields and reject contents in organosolv pulping with organic acid catalysts.. .91
18. Pulp yields and reject contents in organosolv pulping with combination catalysts.. .92
19. Effect of catalysts on pulp production capability in organosolv pulping of
spruce wood at 60 min cook in 80 % methanol 93
20. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with and without catalysts of chloride salts of monovalent cations 99
21. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with catalysts of chloride salts of divalent cations 99
22. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with catalysts of chloride salts of trivalent cations 100
23. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with magnesium salt catalysts 100
24. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with inorganic acid catalysts 101
25. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with organic acid catalysts 101
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26. Residual lignin and viscosity of the pulps and / or undefibrated cooked chips
pulped with combination catalysts 102
27. pH of cooking liquor with and without catalysts of chloride salts of monovalent
cations and the estimated amount of proton generated during the cooking. .106
28. pH of cooking liquor with catalysts of chloride salts of divalent cations and
the estimated amount of proton generated during the cooking 106
29. pH of cooking liquor with catalysts of chloride salts of trivalent cations 107
30. pH of cooking liquor with magnesium-salt catalysts and the estimated
amount of proton generated during the cooking.. 107
31. pH of cooking liquor with inorganic acid catalysts 108
32. pH of cooking liquor with organic acid catalysts 108
33. pH of cooking liquor with combination catalysts and the estimated
amount of proton generated during the cooking 109
34. Sugar composition of pulps and / or undefibrated cooked chips pulped with
and without catalysts of chloride salts of monovalent cations Ill
35. Sugar composition of pulps and / or undefibrated cooked chips pulped with
catalysts of chloride salts of divalent cations 112
36. Sugar composition of pulps and / or undefibrated cooked chips pulped with
catalysts of chloride salts of trivalent cations 112
37. Sugar composition of pulps and / or undefibrated cooked chips pulped with
catalysts of magnesium salts 113
38. Sugar composition of pulps and / or undefibrated cooked chips pulped with
inorganic acid catalysts 113
39. Sugar composition of pulps and / or undefibrated cooked chips pulped with
organic acid catalysts 114
40. Sugar composition of pulps and / or undefibrated cooked chips pulped with
combination catalysts 115
41. Sugar composition of pulps and / or undefibrated cooked chips pulped with
0.050 M CaCl catalyst at different cooking time 116
2
42. Sugar composition of pulps and / or undefibrated cooked chips pulped with
0.025 M CaCl + 0.025 M Mg(N0) catalyst at different cooking times. . . .116
2 3 2
43. Sugar composition of pulps and / or undefibrated cooked chips pulped with
0.025 M A1C1 catalyst at different cooking times 117
3
44. Sugar composition of pulps and / or undefibrated cooked chips pulped with
0.050 M citric acid catalyst at different cooking times 117
45. Sugar composition of kraft pulp and / or undefibrated cooked chips pulped
at different cooking times 118
46. Spent liquor pH and Lignin/Carbohydrate removal in organosolv pulping
with and without catalysts of chloride salts of monovalent cations in
80% methanol 122
47. Spent liquor pH and Lignin/Carbohydrate removal in organosolv pulping
with catalysts of chloride salts of divalent cations in 80 % methanol 122
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