- •Recovered Paper and Recycled Fibers
- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •2006, Isbn 3-527-30997-7
- •Volume 1
- •Isbn: 3-527-30999-3
- •4.1 Introduction 109
- •4.2.5.1 Introduction 185
- •4.3.1 Introduction 392
- •5.1 Introduction 511
- •6.1 Introduction 561
- •6.2.1 Introduction 563
- •6.4.1 Introduction 579
- •Volume 2
- •7.3.1 Introduction 628
- •7.4.1 Introduction 734
- •7.5.1 Introduction 777
- •7.6.1 Introduction 849
- •7.10.1 Introduction 887
- •8.1 Introduction 933
- •1 Introduction 1071
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and
- •1 Introduction 1149
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Isbn: 3-527-30999-3
- •Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •1 Introduction
- •150.000 Annual Fiber Flow[kt]
- •1 Introduction
- •1 Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •Void volume
- •Void volume fraction
- •Xylan and Fiber Morphology
- •Initial bulk residual
- •4.2.5.1 Introduction
- •In (Ai) Model concept Reference
- •Initial value
- •Validation and Application of the Kinetic Model
- •Inititial
- •Viscosity
- •Influence on Bleachability
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Impregnation
- •Introduction
- •International
- •Impregnation
- •Influence of Substituents on the Rate of Hydrolysis
- •140 116 Total so2
- •Xylonic
- •Viscosity Brightness
- •Xyl Man Glu Ara Furf hoAc XyLa
- •Initial NaOh charge [% of total charge]:
- •Introduction
- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •Introduction
- •Introduction
- •Isbn: 3-527-30999-3
- •Introduction
- •Xylosec
- •Xylan residues
- •Viscosity
- •Introduction
- •Viscosity
- •Viscosity
- •Introduction
- •Initiator Promoter Inhibitor
- •Viscosity
- •Viscosity
- •Viscosity
- •Introduction
- •Viscosity
- •Introduction
- •Intra-Stage Circulation and Circulation between Stages
- •Implications of Liquor Circulation
- •Vid Chalmers Tekniska
- •Introduction
- •It is a well-known fact that the mechanical properties of the viscose fibers
- •Increase in the low molecular-weight fraction [2]. The short-chain molecules represent
- •Isbn: 3-527-30999-3
- •In the cooking process or, alternatively, white liquor can be used for the cold
- •Is defined as the precipitate formed upon acidification of an aqueous alkaline solution
- •934 8 Pulp Purification
- •8.2 Reactions between Pulp Constituents and Aqueous Sodium Hydroxide Solution 935
- •Is essentially governed by chemical degradation reactions involving endwise depolymerization
- •80 °C [12]. Caustic treatment: 5%consistency ,
- •30 Min reaction time, NaOh concentrations:
- •8.2 Reactions between Pulp Constituents and Aqueous Sodium Hydroxide Solution
- •80 °C is mainly governed by chemical degradation reactions (e.G. Peeling reaction).
- •Investigated using solid-state cp-mas 13c-nmr spectroscopy (Fig. 8.4).
- •Indicates cleavage of the intramolecular hydrogen bond between o-3-h and o-5′,
- •8 Pulp Purification
- •Interaction between alkali and cellulose, a separate retention tower is not really
- •In the following section.
- •3% In the untreated pulp must be ensured in order to avoid a change in the supramolecular
- •8.3 Cold Caustic Extraction
- •Xylan content [%]
- •8 Pulp Purification
- •Is calculated as effective alkali (ea). Assuming total ea losses (including ea consumption
- •Xylan content [%]
- •8.3 Cold Caustic Extraction
- •120 °C (occasionally 140 °c). As mentioned previously, hce is carried out solely
- •Involved in alkaline cooks (kraft, soda), at less severe conditions and thus avoiding
- •8.4Hot Caustic Extraction 953
- •954 8 Pulp Purification
- •120 Kg NaOh odt–1, 90–240 min, 8.4 bar (abs)
- •8.4Hot Caustic Extraction 955
- •956 8 Pulp Purification
- •Into the purification reaction, either in the same (eo) or in a separate stage
- •960 8 Pulp Purification
- •8.4.1.5 Composition of Hot Caustic Extract
- •8.4Hot Caustic Extraction 961
- •Isbn: 3-527-30999-3
- •Xyloisosaccharinic acid
- •Inorganicsa
- •Inorganic compounds
- •Value (nhv), which better reflects the actual energy release, accounts for the fact
- •968 9 Recovery
- •It should be noted that the recycling of bleach (e.G., oxygen delignification) and
- •9.1 Characterization of Black Liquors 969
- •9.1.2.1 Viscosity
- •9.1.2.3 Surface Tension
- •9.1.2.5 Heat Capacity [8,11]
- •9.2 Chemical Recovery Processes
- •Is described by the empirical equation:
- •9 Recovery
- •Vent gases from all areas of the pulp mill. From an environmental perspective,
- •9.2.2.1 Introduction
- •In the sump at the bottom of the evaporator. The generated vapor escapes
- •Incineration, whereas sulphite ncg can be re-used for cooking acid preparation.
- •9 Recovery
- •Values related to high dry solids concentrations. The heat transfer rate is pro-
- •9.2 Chemical Recovery Processes
- •9.2.2.3 Multiple-Effect Evaporation
- •7% Over effects 4 and 5, but more than 30% over effect 1 alone.
- •9.2 Chemical Recovery Processes
- •Increasing the dry solids concentration brings a number of considerable advantages
- •9.2.2.4 Vapor Recompression
- •Is driven by electrical power. In general, vapor coming from the liquor
- •Vapor of more elevated temperature, thus considerably improving their performance.
- •9 Recovery
- •Is typically around 6 °c. The resulting driving temperature difference
- •Is low, and hence vapor recompression plants require comparatively large heating
- •Vapor recompression systems need steam from another source for start-up.
- •9 Recovery
- •Its temperature is continuously falling to about 180 °c. After the superheaters,
- •In the furnace walls, and only 10–20% in the boiler bank. As water turns into
- •9.2.3.1.2 Material Balance
- •Is required before the boiler ash is mixed. In addition, any chemical make-up
- •In this simplified model, all the potassium from the black liquor (18 kg t–1
- •Values for the chemicals in Eq. (11) can be inserted on a molar basis, equivalent
- •9.2 Chemical Recovery Processes
- •Input/output
- •9 Recovery
- •9.2.3.1.3 Energy Balance
- •In the black liquor, from water formed out of hydrogen in organic material, and
- •9.2 Chemical Recovery Processes
- •9.2.3.2 Causticizing and Lime Reburning
- •9.2.3.2.1 Overview
- •9.2.3.2.2 Chemistry
- •986 9 Recovery
- •Insoluble metal salts are kept low. Several types of filters with and without lime
- •Is, however, not considered a loss because some lime mud must be
- •988 9 Recovery
- •In slakers and causticizers needs special attention in order to avoid particle disintegration,
- •9.2 Chemical Recovery Processes 989
- •Ing disks into the center shaft, and flows to the filtrate separator. There, the white
- •9.2.3.2.4 Lime Cycle Processes and Equipment
- •It is either dried with flue gas in a separate, pneumatic lime mud dryer or is fed
- •990 9 Recovery
- •Its temperature falls gradually. Only about one-half of the chemical energy in the
- •9.2.3.3.2 Black Liquor Gasification
- •Inorganics leave the reactor as solids, and into high-temperature techniques,
- •In the bed. Green liquor is produced from surplus bed solids. The product gas
- •992 9 Recovery
- •Incremental capacity for handling black liquor solids. The encountered difficulties
- •10% Of today’s largest recovery boilers. When the process and material issues are
- •9.2 Chemical Recovery Processes 993
- •9.2.3.3.3 In-Situ Causticization
- •Is still in the conceptual phase, and builds on the formation of sodium titanates
- •9.2.3.3.4 Vision Bio-Refinery
- •Into primary and secondary recovery steps. This definition relates to the recovery
- •994 9 Recovery
- •Is largely different between sulfite cooking bases. While magnesium and
- •Introduction
- •In alkaline pulping the operation of the lime kiln represents an emission source.
- •Isbn: 3-527-30999-3
- •Is by the sophisticated management of these sources. This comprises their collection,
- •Ions, potassium, or transition metals) in the process requires the introduction
- •Industry”. Similarly guidelines for a potential kraft pulp mill in Tasmania [3]
- •Initially, the bleaching of chemical pulp was limited to treatment with hypochlorite
- •In a hollander, and effluent from the bleach plant was discharged without
- •In a heh treatment and permitted higher brightness at about 80% iso (using
- •Increasing pulp production resulted in increasing effluent volumes and loads.
- •10.2 A Glimpse of the Historical Development 999
- •It became obvious that the bleaching process was extremely difficult to operate in
- •In a c stage was detected as aox in the effluent (50 kg Cl2 t–1 pulp generated
- •1% Of the active chlorine is converted into halogenated compounds (50 kg active
- •In chlorination effluent [12] led to the relatively rapid development of alternative
- •1000 10 Environmental Aspects of Pulp Production
- •10.2 A Glimpse of the Historical Development
- •In 1990, only about 5% of the world’s bleached pulp was produced using ecf
- •64 Million tons of pulp [14]. The level of pulp still bleached with chlorine
- •10 000 Tons. These are typically old-fashioned, non-wood mills pending an
- •In developed countries, kraft pulp mills began to use biodegradation plants for
- •10 Environmental Aspects of Pulp Production
- •Indeed, all processes are undergoing continual development and further improvement.
- •Vary slightly different depending upon the type of combustion unit and the fuel
- •10.3Emissions to the Atmosphere
- •Volatile organic
- •In 2004 for a potential pulp mill in Tasmania using “accepted
- •10 Environmental Aspects of Pulp Production
- •Is woodyard effluent (rain water), which must be collected and treated biologically
- •10.4 Emissions to the Aquatic Environment
- •Is converted into carbon dioxide, while the other half is converted into biomass
- •Into alcohols and aldehydes; (c) conversion of these intermediates into acetic acid and
- •10 Environmental Aspects of Pulp Production
- •In North America, effluent color is a parameter which must be monitored.
- •It is not contaminated with other trace elements such as mercury, lead, or cadmium.
- •10.6 Outlook
- •Increase pollution by causing a higher demand for a chemical to achieve identical
- •In addition negatively affect fiber strength, which in turn triggers a higher
- •Introduction
- •2002, Paper-grade pulp accounts for almost 98% of the total wood pulp production
- •Important pulping method until the 1930s) continuously loses ground and finds
- •Importance in newsprint has been declining in recent years with the increasing
- •Isbn: 3-527-30999-3
- •Virtually all paper and paperboard grades in order to improve strength properties.
- •In fact, the word kraft is the Swedish and German word for strength. Unbleached
- •Importance is in the printing and writing grades. In these grades, softwood
- •In this chapter, the main emphasis is placed on a comprehensive discussion of
- •1010 11 Pulp Properties and Applications
- •Is particularly sensitive to alkaline cleavage. The decrease in uronic acid content
- •Xylan in the surface layers of kraft pulps as compared to sulfite pulps has been
- •80% Cellulose content the fiber strength greatly diminishes [14]. This may be due
- •Viscoelastic and capable of absorbing more energy under mechanical stress. The
- •11.2 Paper-Grade Pulp 1011
- •Various pulping treatments using black spruce with low fibril
- •In the viscoelastic regions. Fibers of high modulus and elasticity tend to peel their
- •1012 11 Pulp Properties and Applications
- •11.2 Paper-Grade Pulp
- •Viscosity mL g–1 793 635 833 802 1020 868 1123
- •Xylose % od pulp 7.3 6.9 18.4 25.5 4.1 2.7 12.2
- •11 Pulp Properties and Applications
- •Inorganic Compounds
- •11.2 Paper-Grade Pulp
- •Insight into many aspects of pulp origin and properties, including the type of
- •Indicate oxidative damage of carbohydrates).
- •In general, the r-values of paper pulps are typically at higher levels as predicted
- •Is true for sulfite pulps. Even though the r-values of sulfite pulps are generally
- •Is rather unstable in acid sulfite pulping, and this results in a low (hemicellulose)
- •11 Pulp Properties and Applications
- •Ing process, for example the kraft process, the cellulose:hemicellulose ratio is
- •Increases by up to 100%. In contrast to fiber strength, the sheet strength is highly
- •Identified as the major influencing parameter of sheet strength properties. It has
- •In contrast to dissolving pulp specification, the standard characterization of
- •Is observed for beech kraft pulp, which seems to correlate with the enhanced
- •11.2 Paper-Grade Pulp
- •11 Pulp Properties and Applications
- •Is significantly higher for the sulfite as compared to the kraft pulps, and indicates
- •11.2 Paper-Grade Pulp
- •Xylan [24].
- •11 Pulp Properties and Applications
- •11.2 Paper-Grade Pulp
- •11 Pulp Properties and Applications
- •Introduction
- •Various cellulose-derived products such as regenerated fibers or films (e.G.,
- •Viscose, Lyocell), cellulose esters (acetates, propionates, butyrates, nitrates) and
- •In pulping and bleaching operations are required in order to obtain a highquality
- •Important pioneer of cellulose chemistry and technology, by the statement that
- •11.3 Dissolving Grade Pulp
- •Involves the extensive characterization of the cellulose structure at three different
- •Is an important characteristic of dissolving pulps. Finally, the qualitative and
- •Inorganic compounds
- •11 Pulp Properties and Applications
- •11.3.2.1 Pulp Origin, Pulp Consumers
- •Include the recently evaluated Formacell procedure [7], as well as the prehydrolysis-
- •11.3 Dissolving Grade Pulp
- •Viscose
- •11 Pulp Properties and Applications
- •11.3.2.2 Chemical Properties
- •11.3.2.2.1 Chemical Composition
- •In the polymer. The available purification processes – particularly the hot and cold
- •11.3 Dissolving Grade Pulp
- •In the steeping lye inhibits cellulose degradation during ageing due to the
- •Is governed by a low content of noncellulosic impurities, particularly pentosans,
- •Increase in the xylan content in the respective viscose fibers clearly support the
- •11.3 Dissolving Grade Pulp
- •Instability. Diacetate color is measured by determining the yellowness coefficient
- •Xylan content [%]
- •11 Pulp Properties and Applications
- •Xylan content [%]
- •11.3 Dissolving Grade Pulp
- •11.3 Dissolving Grade Pulp
- •Is, however, not the only factor determining the optical properties of cellulosic
- •In the case of alkaline derivatization procedures (e.G., viscose, ethers). In industrial
- •11.3 Dissolving Grade Pulp
- •Viscose
- •Viscose
- •In order to bring out the effect of mwd on the strength properties of viscose
- •Imitating the regular production of rayon fibers. To obtain a representative view
- •11 Pulp Properties and Applications
- •Viscose Ether (hv) Viscose Acetate Acetate
- •Xylan % 3.6 3.1 1.5 0.9 0.2
- •1.3 Dtex regular viscose fibers in the conditioned
- •11.3 Dissolving Grade Pulp
- •Is more pronounced for sulfite than for phk pulps. Surprisingly, a clear correlation
- •Viscose fibers in the conditioned state related to the carbonyl
- •1038 11 Pulp Properties and Applications
- •In a comprehensive study, the effect of placing ozonation before (z-p) and after
- •Increased from 22.9 to 38.4 lmol g–1 in the case of a pz-sequence, whereas
- •22.3 To 24.2 lmol g–1. The courses of viscosity and carboxyl group contents were
- •Viscosity measurement additionally induces depolymerization due to strong
- •11 Pulp Properties and Applications
- •Increasing ozone charges. For more detailed
- •11.3 Dissolving Grade Pulp
- •Is more selective when ozonation represents the final stage according to an
- •11.3.2.3 Supramolecular Structure
- •1042 11 Pulp Properties and Applications
- •Is further altered by subsequent bleaching and purification processes. This
- •Involved in intra- and intermolecular hydrogen bonds. The softened state favors
- •11.3 Dissolving Grade Pulp
- •Interestingly, the resistance to mercerization, which refers to the concentration of
- •11 Pulp Properties and Applications
- •Illustrate that the difference in lye concentration between the two types of dissolving
- •Intensity (see Fig. 11.18: hw-phk high p-factor) clearly changes the supramolecular
- •11.3 Dissolving Grade Pulp
- •Viscose filterability, thus indicating an improved reactivity.
- •11 Pulp Properties and Applications
- •Impairs the accessibility of the acetylation agent. When subjecting a low-grade dissolving
- •Identification of the cell wall layers is possible by the preferred orientation of
- •Viscose pulp (low p-factor) (Fig. 11.21b, top). Apparently, the type of pulp – as well
- •11 Pulp Properties and Applications
- •150 °C for 2 h, more than 70% of a xylan, which was added to the cooking liquor
- •20% In the case of alkali concentrations up to 50 g l–1 [67]. Xylan redeposition has
- •11.3 Dissolving Grade Pulp
- •Xylan added linters cooked without xylan linters cooked with xylan
- •Viscosity
- •In the surface layer than in the inner fiber wall. This is in agreement with
- •11 Pulp Properties and Applications
- •Xylan content in peelings [wt%]
- •Xylan content located in the outermost layers of the beech phk fibers suggests
- •11.3.2.5 Fiber Morphology
- •11 Pulp Properties and Applications
- •50 And 90%. Moreover, bleachability of the screened pulps from which the wood
- •11.3.2.6 Pore Structure, Accessibility
- •11.3 Dissolving Grade Pulp
- •Volume (Vp), wrv and specific pore surface (Op) were seen between acid sulfite
- •11 Pulp Properties and Applications
- •Irreversible loss of fiber swelling occurs; indeed, Maloney and Paulapuro reported
- •In microcrystalline areas as the main reason for hornification [85]. The effect of
- •105 °C, thermal degradation proceeds in parallel with hornification, as shown in
- •Increased, particularly at temperatures above 105 °c. The increase in carbonyl
- •In pore volume is clearly illustrated in Fig. 11.28.
- •11.3 Dissolving Grade Pulp
- •Viscosity
- •11 Pulp Properties and Applications
- •Increase in the yellowness coefficient, haze, and the amount of undissolved particles.
- •11.3.2.7 Degradation of Dissolving Pulps
- •In mwd. A comprehensive description of all relevant cellulose degradation processes
- •Is reviewed in Ref. [4]. The different modes of cellulose degradation comprise
- •11.3 Dissolving Grade Pulp
- •50 °C, is illustrated graphically in Fig. 11.29.
- •11 Pulp Properties and Applications
- •In the crystalline regions.
- •11.3 Dissolving Grade Pulp
- •Important dissolving pulps, derived from hardwood, softwood and cotton linters
- •11.3 Dissolving Grade Pulp 1061
- •Xylan rel% ax/ec-pad 2.5 3.5 1.3 1.0 3.2 0.4
- •Viscosity mL g–1 scan-cm 15:99 500 450 820 730 1500 2000
- •1062 11 Pulp Properties and Applications
- •Isbn: 3-527-30999-3
- •Introduction
- •Isbn: 3-527-30999-3
- •1072 1 Introduction
- •Isbn: 3-527-30999-3
- •Inventor of stone groundwood. Right: the second version
- •1074 2 A Short History of Mechanical Pulping
- •In refining, the thinnings (diameter 7–10cm) can also be processed.
- •In mechanical pulping as it causes foam; the situation is especially
- •In mechanical pulping, those fibers that are responsible for strength properties
- •Isbn: 3-527-30999-3
- •In mechanical pulping, the wood should have a high moisture content, and the
- •In the paper and reduced paper quality. The higher the quality of the paper, the
- •1076 3 Raw Materials for Mechanical Pulp
- •1, Transversal resistance; 2, Longitudinal resistance; 3, Tanning limit.
- •3.2 Processing of Wood 1077
- •In the industrial situation in order to avoid problems of pollution and also
- •1078 3 Raw Materials for Mechanical Pulp
- •2, Grinder pit; 3, weir; 4, shower water pipe;
- •5, Wood magazine; 6, finger plate; 7, pulp stone
- •Isbn: 3-527-30999-3
- •4.1.2.1 Softening of the Fibers
- •1080 4 Mechanical Pulping Processes
- •235 °C, whereas according to Styan and Bramshall [4] the softening temperatures
- •Isolated lignin, the softening takes place at 80–90 °c, and additional water
- •4.1 Grinding Processes 1081
- •1082 4 Mechanical Pulping Processes
- •1, Cool wood; 2, strongly heated wood layer; 3, actual grinding
- •4.1.2.2 Defibration (Deliberation) of Single Fibers from the Fiber Compound
- •4 Mechanical Pulping Processes
- •Influence of Parameters on the Properties of Groundwood
- •In the mechanical defibration of wood by grinding, several process parameters
- •Improved by increasing both parameters – grinding pressure and pulp stone
- •In practice, the temperature of the pit pulp is used to control the grinding process,
- •In Fig. 4.8, while the grit material of the pulp stone estimates the microstructure
- •4 Mechanical Pulping Processes
- •4.1 Grinding Processes
- •Is of major importance for process control in grinding.
- •4 Mechanical Pulping Processes
- •4.1.4.2 Chain Grinders
- •Is fed continuously, as shown in Fig. 4.17.
- •Initial thickness of the
- •75 Mm thickness, is much thinner than that of a concrete pulp stone, much
- •4 Mechanical Pulping Processes
- •Include:
- •Increases; from the vapor–pressure relationship, the boiling temperature is seen
- •4 Mechanical Pulping Processes
- •In the pgw proves, and to prevent the colder seal waters from bleeding onto the
- •4.1 Grinding Processes
- •In pressure grinding, the grinder shower water temperature and flow are
- •70 °C, a hot loop is no longer used, and the grinding process is
- •4 Mechanical Pulping Processes
- •Very briefly at a high temperature and then refined at high
- •4.2 Refiner Processes
- •4 Mechanical Pulping Processes
- •Intensity caused by plate design and rotational speed.
- •4.2 Refiner Processes
- •1. Reduction of the chips sizes to units of matches.
- •2. Reduction of those “matches” to fibers.
- •3. Fibrillation of the deliberated fibers and fiber bundles.
- •1970S as result of the improved tmp technology. Because the key subprocess in
- •4 Mechanical Pulping Processes
- •Impregnation Preheating Cooking Yield
- •30%. Because of their anatomic structure, hardwoods are able to absorb more
- •Is at least 2 mWh t–1 o.D. Pulp for strongly fibrillated tmp and ctmp pulps from
- •4 Mechanical Pulping Processes
- •4.2 Refiner Processes
- •1500 R.P.M. (50 Hz) or 1800 r.P.M. (60 Hz); designed pressure 1.4 mPa
- •1500 R.P.M. (50 Hz) or 1800 r.P.M. (60 Hz); designed pressure 1.4 mPa;
- •4.2 Refiner Processes
- •4 Mechanical Pulping Processes
- •In hardwoods makes them more favorable than softwoods for this purpose. A
- •4.2 Refiner Processes
- •Isbn: 3-527-30999-3
- •1114 5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.2Machines and Aggregates for Screening and Cleaning 1115
- •In refiner mechanical pulping, there is virtually no such coarse material in the
- •1116 5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.2Machines and Aggregates for Screening and Cleaning
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5 Processing of Mechanical Pulp and Reject Handling: Screening and Cleaning
- •5.3 Reject Treatment and Heat Recovery
- •55% Iso and 65% iso. The intensity of the bark removal, the wood species,
- •Isbn: 3-527-30999-3
- •1124 6 Bleaching of Mechanical Pulp
- •Initially, the zinc hydroxide is filtered off and reprocessed to zinc dust. Then,
- •2000 Kg of technical-grade product is common. Typically, a small amount of a chelant
- •6.1 Bleaching with Dithionite 1125
- •Vary, but are normally ca. 10 kg t–1 or 1% on fiber. As the number of available
- •1126 6 Bleaching of Mechanical Pulp
- •6.2 Bleaching with Hydrogen Peroxide
- •70 °C, 2 h, amount of NaOh adjusted.
- •6.2 Bleaching with Hydrogen Peroxide
- •Is shown in Fig. 6.5, where silicate addition leads to a higher brightness and a
- •Volume (bulk). For most paper-grade applications, fiber volume should be low in
- •Valid and stiff fibers with a high volume are an advantage; however, this requires
- •1130 6 Bleaching of Mechanical Pulp
- •6.2 Bleaching with Hydrogen Peroxide
- •Very high brightness can be achieved with two-stage peroxide bleaching, although
- •In a first step. This excess must be activated with an addition of caustic soda. The
- •Volume of liquid to be recycled depends on the dilution and dewatering conditions
- •6 Bleaching of Mechanical Pulp
- •6 Bleaching of Mechanical Pulp
- •Is an essential requirement for bleaching effectiveness. Modern twin-wire presses
- •Is discharged to the effluent treatment plant. After the main bleaching stage, the
- •6.3 Technology of Mechanical Pulp Bleaching
- •1136 6 Bleaching of Mechanical Pulp
- •Isbn: 3-527-30999-3
- •7.3 Shows the fractional composition according to the McNett principle versus
- •1138 7 Latency and Properties of Mechanical Pulp
- •7.2 Properties of Mechanical Pulp 1139
- •Isbn: 3-527-30999-3
- •In 1950, about 50% of the global paper production was produced. This proportion
- •4.0% Worldwide; 4.2% for the cepi countries; and 4.8% for Germany.
- •1150 1 Introduction
- •1 Introduction
- •1 Introduction
- •Virgin fibers
- •74.4 % Mixed grades
- •Indonesia
- •Virgin fibers
- •Inhomogeneous sample Homogeneous sample
- •Variance of sampling Variance of measurement
- •1.Quartile
- •3.Quartile
- •Insoluble
- •Insoluble
- •Insoluble
- •Integral
- •In Newtonion liquid
- •Velocity
- •Increasing dp
- •2Α filter
- •0 Reaction time
- •Increasing interaction of probe and cellulose
- •Increasing hydrodynamic size
- •Vessel cell of beech
- •Initial elastic range
- •Internal flow
- •Intact structure
- •Viscosity 457
- •Isbn: 3-527-30999-3
- •1292 Index
- •Visbatch® pulp 354
- •Index 1293
- •1294 Index
- •Impregnation 153
- •Viscosity–extinction 433
- •Index 1295
- •1296 Index
- •Index 1297
- •Inhibitor 789
- •1298 Index
- •Index 1299
- •Impregnation liquor 290–293
- •1300 Index
- •Industries
- •Index 1301
- •1302 Index
- •Index 1303
- •Xylose 463
- •1304 Index
- •Index 1305
- •1306 Index
- •Index 1307
- •1308 Index
- •In conventional kraft cooking 232
- •Visbatch® pulp 358
- •Index 1309
- •In prehydrolysis-kraft process 351
- •Visbatch® cook 349–350
- •1310 Index
- •Index 1311
- •1312 Index
- •Viscosity 456
- •Index 1313
- •Viscosity 459
- •Interactions 327
- •1314 Index
- •Index 1315
- •Viscosity 459
- •1316 Index
- •Index 1317
- •Xylose 461
- •Index 1319
- •Visbatch® pulp 355
- •Impregnation 151–158
- •1320 Index
- •Index 1321
- •1322 Index
- •Xylan water prehydrolysis 333
- •Index 1323
- •1324 Index
- •Viscosity 459
- •Index 1325
- •Xylose 940
- •1326 Index
- •Index 1327
- •In selected kinetics model 228–229
- •4OMeGlcA 940
- •1328 Index
- •Index 1329
- •Intermediate molecule 164–165
- •1330 Index
- •Viscosity 456
- •Index 1331
- •1332 Index
- •Impregnation liquor 290–293
- •Index 1333
- •1334 Index
- •Index 1335
- •1336 Index
- •Impregnation 153
- •Index 1337
- •1338 Index
- •Viscose process 7
- •Index 1339
- •Volumetric reject ratio 590
- •1340 Index
- •Index 1341
- •1342 Index
- •Index 1343
- •1344 Index
- •Index 1345
- •Initiator 788
- •Xylose 463
- •1346 Index
- •Index 1347
- •Vessel 385
- •Index 1349
- •1350 Index
- •Xylan 834
- •1352 Index
Xylonic
acid
Methanol
total total mon olig mon olig mon olig mon olig mon olig
[% odw] [% odw] [% odw] [% odw] [% odw] [% odw] [% odw] [% odw]
0
Mg 433 18 7.3 6.3 0.2 3.9 0.4 0.0 0.3 0.5 0.0 0.0 0.1 0.4 0.1 2.0 0.4 0.2
Mg 434 37 12.2 13.4 0.9 7.1 0.3 0.0 0.2 0.6 0.0 0.2 0.1 0.5 0.1 3.5 0.8 0.4
Mg 435 60 15.0 17.9 2.7 7.2 0.2 0.0 0.3 0.5 0.0 0.4 0.2 0.4 0.2 4.6 0.8 0.5
Mg 436 90 17.1 21.8 6.0 4.6 0.2 0.0 0.4 0.3 0.1 0.2 0.4 0.3 0.3 5.6 1.6 0.6
Mg 437 130 18.6 23.8 9.0 1.0 0.2 0.0 0.7 0.2 0.4 0.1 0.6 0.0 0.5 6.1 3.1 0.7
Mg 438 160 21.2 24.1 10.8 0.2 0.2 0.0 1.0 0.2 0.5 0.3 0.6 0.0 0.8 6.5 4.0 0.7
Mg 439 180 21.5 24.1 10.7 0.0 0.2 0.0 1.1 0.1 0.6 0.2 0.6 0.0 1.0 6.9 3.7 0.9
Mg 420 210 21.6 24.2 10.4 0.0 0.2 0.0 1.4 0.0 0.8 0.0 0.6 0.0 1.1 7.0 3.6 0.9
M 408 249 21.8 24.2 9.7 0.0 0.1 0.0 1.9 0.0 0.9 0.0 0.7 0.0 1.4 6.8 3.7 0.9
0 50 100 150 200 250
0
5
10
15
20
25
Dissolved carbohydrate derived
compounds [% odw]
H-Factor
Xylose Arabinose Glucose Mannose
Galactose Furfural Acetic Acid
Xylonic Acid Methanol
Fig. 4.170 Course of dissolved carbohydrate
derived components present in the spent
liquor from beech dissolving pulp production
using the magnesium sulfite process [13].
Cooking conditions comprise a total SO2
concentration of 0.76 mol L–1, a free SO2 concentration
of 0.32 mol L–2 free SO2, a liquor-towood
ratio of 2.4:1, and a cooking temperature
of 148 °C.
when the hydrogen sulfite ion concentration is very low, only little or no aldonic
acids are formed. Consequently, the amount of combined SO2 regulates the yield
of the aldonic acid formation. As expected from the carbohydrate composition of
the applied wood species, the spent liquor from hardwood cooks contains predominantly
xylonic acid, whereas mannonic and xylonic acid are almost equally present
in the spent liquor from a softwood sulfite cook. The compositions of both the
pulp and spent liquor of dissolving pulp production from spruce and beech wood
are listed in Tab. 4.60. This comparison is based on a viscosity of 700 mL g–1 for
both pulps. As the free SO2 concentration is approximately 20% lower for the
spruce as compared to the beech sulfite cook, the ratio of aldoses-to-aldonic acids
is slightly shifted to a higher aldonic acid concentration in case of the former.
4.3 Sulfite Chemical Pulping 447
Tab. 4.60 Pulp and spent liquor compositions of both beech and
spruce sulfite cooks for the production of a dissolving pulp with
an intrinsic viscosity of 700 mL g–1 (according to [14]).
Parameters unit Beech Spruce
Cooking conditions
Total SO2 mol L–1 0.76 0.74
Free SO2 mol L–1 0.32 0.26
Temperature °C 148 145
H-Factor 191 306
Pulp
Yield % 44.9 45.9
Viscosity mL g–1 700 700
Kappa number 5.0 3.5
R10-content % 86.6 88.1
R18-content % 90.8 91.1
Xylan % 5.5 3.1
Mannan % 0.4 2.8
Spent liquor
Xylose g kg od w–1 100.9 18.4
Mannose g kg od w–1 7.0 58.1
Glucose g kg od w–1 8.4 19.8
Galactose g kg od w–1 4.8 n.d.
Arabinose g kg od w–1 1.6 0.6
Rhamnose g kg od w–1 2.8 <0.4
Furfural g kg od w–1 9.8 2.3
Acetic acid g kg od w–1 61.7 26.8
Xylonic acid g kg od w–1 29.6 15.5
Mannonic acid g kg od w–1 <0.5 20.2
n.d. = not determined.
448 4 Chemical Pulping Processes
The total hemicellulose content is equal for both pulps. However, the xylan-tomannan
ratio changes during spruce sulfite cooking from 0.55:1 in the wood to
1.1:1 in the pulp. This change in carbohydrate ratio is also reflected in the spent
liquor composition, where the xylose-to-mannose ratio comprises a value of
0.32:1, indicating a higher resistance of the arabinoxylan as compared to the glucomannan
towards acid hydrolysis. The lower furfural and acetic acid concentrations
in the spent liquor of the spruce acid sulfite cook can be attributed to both
the lower amount of pentoses and acetyl groups substituted at the C-2 and C-3
positions in mannose and glucose units of the glucomannan in spruce.
4.3.5.2 Influence of Reaction Conditions
Knowledge of the chemistry and technology of sulfite pulping up to the year 1965
has been reviewed in detail by Rydholm [20]. In the following sections, only the
most recent data relating to sulfite pulping are presented, with the main focus
centered on dissolving pulp manufacture.
4.3.5.2.1 Wood Species
The wood raw material has a decisive influence on the processability and final
pulp quality. The heterogeneous nature of the wood structure and the chemical
and physical differences between and within wood species are reflected in all
pulping processes. Acid sulfite pulping technology is known to be the most sensitive
process to the properties of the wood raw material, and many softwood species
– and also some hardwoods – are considered to be less suited to acid sulfite
pulping. The deficiencies involved with acid sulfite pulping of, for example pines
or larches, are high screenings, a high residual lignin content, and thus a low
screened yield. The poor pulping results are connected with either the presence of
certain extractives in the wood, especially in the heartwood, or limited impregnation
due to a dense wood structure. It has been found that phenolic resins – such
as pinosylvin in pine heartwood or taxifolin in Douglas fir – react with lignin in
acid sulfite liquors to form a condensation product that prevents delignification
[24–27]. Moreover, taxifolin tends to reduce hydrogen sulfite ions to thiosulfate
ions, thereby decreasing the stability of the sulfite cooking liquor [28].
Subsequently, much effort has been undertaken to modify the sulfite cooking
process to overcome the problems encountered with the use of resinous wood. It
was found that pretreatment of the wood with a sulfite cooking liquor of moderate
acidity, as with a pure hydrogen sulfite solution, and low temperature will favor
sulfonation of the reactive groups of the lignin over condensation reactions with
the phenolic resins. Another prerequisite of selective sulfonation comprises an
efficient pressure impregnation. This initial sulfonation stage is then followed by
a conventional acid sulfite cook at temperatures and H-factors selected according
to the grade desired. Hence, two-stage sulfite pulping with a preceding sulfonation
stage at low acidity or even neutral pH conditions makes possible the use of
pines and larches.
4.3 Sulfite Chemical Pulping 449
In the case of conventional and more simple one-stage acid sulfite pulping processes,
only a limited amount of wood species can be used. Most appropriate are
hardwoods with low resin contents and high density such as beech wood (Fagus
sylvatica) and certain eucalyptus species (E. globulus, E. saligna, E.urograndis, etc.).
Dense hardwoods with a low lignin content are favorable because of the high specific
pulp yield related to the volume of the digester. Replacing spruce with, for
example beech wood, results in an almost 50% higher yield at a given digester
volume (280 kg o.d. beech versus 190 kg o.d. spruce per m3 digester, respectively).
In the following section, four representative hardwoods – beech (Fagus sylvatica),
aspen (Populus tremulus), eucalypt (E. globulus) and birch (Betula pendula)
and one softwood species, spruce (Picea abies) – which together constitute the
most important wood raw material for acid sulfite pulping, are evaluated comparatively
with respect to their processability and unbleached pulp quality.
The chemical composition of the wood determines very important parameters
such as pulp yield and pulp properties. The purity of dissolving pulps is governed
by the content of noncellulosic carbohydrates and other impurities such as resins
or inorganic components of the wood raw material used.
Chemical analysis of the hardwood samples reveals high glucan and low xylan
contents for aspen and eucalypt. The low glucan and high xylan contents of birch
and beech, however, indicate low cellulose yield at high residual xylan contents in
the resulting dissolving pulps. Among the hardwood species, aspens shows a surprisingly
high mannose content. Spruce, as the only representative of softwoods
in this comparison, contains a relatively high glucan content and, together with
eucalypt, the lowest amount of hemicelluloses among the species investigated.
The hardwoods are characterized by a low and rather constant Klason lignin content
ranging from 18.9% to 21.0%, and by a high acid-soluble lignin content, with
the highest value by far determined for eucalypt. The low lignin content of the
hardwoods indicates a more efficient delignification as compared to spruce at given
cooking conditions.
The highest DCM-extractives contents were measured for birch and aspen, but
this may relate to a pitch problem during further processing of the corresponding
unbleached pulps.
Based on the chemical analysis of the main wood components, the highest cellulose
yields and cellulose purities can be expected for aspen and eucalypt. The
results of the chemical analysis of selected wood chips are detailed in Tab. 4.61
(see also Tab. 4.49).
The introduced five wood species were subjected to one-stage acid sulfite pulping
according to the procedure described in Section 4.3.5.1 (see also Fig. 4.157).
The cooking conditions applied namely the impregnation procedure, the cooking
acid composition, the liquor-to-wood ratios and the maximum cooking temperatures
were identical for beech, aspen, and eucalypt and comparable for spruce and
birch (Tab. 4.62). The slightly different cooking acid compositions in the case of
birch and spruce can be classified as rather insignificant with respect to their ion
product, [H+]·[HSO3
– ], which determines the rate of delignification.
450 4 Chemical Pulping Processes
Tab. 4.61 Chemical composition of beech, aspen, eucalyptus,
birch and spruce as used for the cooking experiments
(according to [14]).
Beech
Fagus sylvatica
Aspen
Populus tremulus
Eucalypt
E. globulus
Birch
Betula pendula
Spruce
Picea abies
Carbohydrates 72.8 75.2 71.8 73.6 70.0
Glucose 42.6 49.9 48.1 39.7 45.7
Xylose 19.5 15.9 14.5 22.1 6.6
Arabinose 0.7 0.1 0.5 0.5 1.0
Galactose 0.8 0.4 1.5 1.0 1.6
Mannose 1.1 2.6 0.5 1.3 12.0
Rhamnose 0.5 0.1 0.5 0.3
Acetyl 4.5 3.7 3.4 5.1 1.4
Uronic acid 3.1 2.5 2.7 3.5 1.8
Lignin 24.5 22.0 26.2 23.3 27.2
Klason 21.0 18.9 20.6 19.7 27.0
Acid–soluble 3.5 3.1 5.6 3.6 0.2
Extractives 1.8 1.0 0.2 1.9 1.0
DCM 0.2 1.0 0.2 1.9 1.0
Et-OH 1.6 n.a. n.a. n.a.
Ash 0.4 0.3 0.3 0.3 0.2
Total 99.5 98.5 98.5 99.0 98.5
n.a. = not applicable.
The main target parameter for dissolving pulp production is the average molecular
weight of the polysaccharide fraction, expressed as the CED-intrinsic viscosity;
this was adjusted solely by the H-factor. All other parameters were kept constant.
The relationships between viscosity and H-factor indicate the depolymerization
behavior of the investigated wood species, which is an important criterion in
case of blending of wood chips. The data in Fig. 4.171 show that beech, aspen and
birch show virtually the same degradation characteristics, whereas (surprisingly)
eucalyptus is ahead and spruce behind their course of viscosity degradation. The
higher resistance towards cellulose degradation of spruce can be explained by its
higher lignin content.
4.3 Sulfite Chemical Pulping 451
Tab. 4.62 Important cooking parameters applied in the course of
one-stage acid sulfite cooking of beech, aspen, eucalyptus, birch
and spruce (according to [14]).
Wood
species
RSO2
[mol L–1]
Free SO2
[mol L–1]
[H+]*[HSO3]
at 25 °C, t = 0
I:s
ratio
Temperature
[ °C]
Beech 1.04 0.68 0.0104 2.7 138
Aspen 1.05 0.69 0.0105 2.7 138
Eucalypt 1.05 0.68 0.0104 2.7 138
Birch 0.88 0.51 0.0078 2.5 145
Spruce 1.07 0.59 0.0091 3.2 145
0 50 100 150 200 250 300
0
200
400
600
800
1000
1200
Beech Aspen Eucalyptus Birch Spruce
Viscosity [ml/g]
H-Factor
Fig. 4.171 Impact of H-factor during one-stage acid sulfite
cooking of beech, aspen, eucalyptus, birch, and spruce on the
viscosity of the unbleached pulps (according to [14]). For
cooking conditions, see Tab. 4.62.
Among the wood species investigated, aspen shows by far the best delignification
selectivity (expressed in terms of viscosity–kappa number relationship), followed
by spruce, beech, eucalyptus and, at some distance, birch (see Fig. 4.172).
452 4 Chemical Pulping Processes
0 3 6 9 12 15 18
200
400
600
800
1000
Beech Aspen Eucalyptus Birch Spruce
Viscosity [ml/g]
Kappa number
Fig. 4.172 Delignification selectivity illustrated as viscosity–
kappa number relationship of unbleached acid sulfite pulps
made from beech, aspen, eucalyptus, birch, and spruce
(according to [14]). For cooking conditions, see Tab. 4.62.
The limited extent of the delignification of birch wood may be attributed to a
dense wood structure and the high content of extractives which can generate
cross-links with lignin during acid sulfite pulping, thereby inhibiting the delignification.
The fines contain a disproportionately high lignin and extractives content.
Thus, removal of the fine fibers from pulp decreases the resin content of the
remaining pulp [29]. The residual kappa number is unexpectedly high in the case
of eucalyptus. It can be assumed that – at the given pulping conditions – the ratio
of hydrolysis to sulfonation reactions is slightly shifted to the former in the case
of eucalyptus. This assumption is also supported by the low degree of sulfonation,
which amounts only 0.60 S/OCH3 for eucalyptus in comparison to 0.73 for beech
and even 0.88 for aspen, respectively. Another reason for the impaired delignification
selectivity might be the accelerated cellulose degradation due to a better accessibility
as compared to the other wood species.
The screened yields at given kappa numbers are highest for aspen pulp, followed
by eucalyptus, spruce and with relatively clear distance beech and birch.
This can be expected, as the pulp yields are in proportion to the glucan content of
the respective wood species. The dependence of screened yield on kappa number
is shown graphically in Fig. 4.173. Viscosity degradation during the final cooking
phase is clearly connected to yield losses. The slopes of the viscosity dependent
upon yield losses were comparable for all wood species investigated, and ranged
from 0.7% to 0.9% per reduction of 100 intrinsic viscosity units (mL g–1).
4.3 Sulfite Chemical Pulping 453
0 200 400 600 800 1000 1200
36
39
42
45
48
51
54
Beech Aspen Eucalypt Birch Spruce
Screened Yield [%]
Viscosity [ml/g]
Fig. 4.173 Screened yield as a function of viscosity of the
unbleached acid sulfite pulps made from beech, aspen, eucalyptus,
birch, and spruce (according to [14]). For cooking conditions,
see Tab. 4.62.
As the quality of dissolving pulps is closely related to its impurities, the content
of noncellulosic carbohydrates (originating from the wood hemicelluloses) in relation
to pulp viscosity is an important criterion for dissolving pulp production.
Xylan, the predominant hemicellulose in hardwoods, is thus related to the viscosity
of the unbleached pulps (Fig. 4.174). However, at a target pulp viscosity (e.g.,
700 mL g–1), the xylan contents of the unbleached pulps are not exactly in proportion
to the xylan contents of the respective wood species. The eucalypt pulp contains
a higher xylan content compared to the aspen pulp, possibly due to both an
accelerated cellulose degradation and a more resistant xylan of the former. Indeed,
a slightly higher uronic acid content of the xylan backbone of the eucalypt xylan
may be responsible for the less reactive b–1,4-glycosidic bonds within the xylan
polymer [30,31]. Furthermore, the xylan content in the spruce pulp is higher in
relation to the xylan contents of the hardwood pulps and, as would have been
expected, from the xylan content in the wood.
The recovery of wood-based by-products being dissolved in the cooking liquor
becomes an increasingly important criterion for the evaluation of modern pulping
technologies. The results can be interpreted as a mirror-image of unbleached pulp
yields – the higher the unbleached pulp yield, the lower the yield of carbohydratederived
by-products.
The cooking liquors from hardwood acid sulfite pulping are dominated by the
degradation products derived from pentosans such as xylose, arabinose, xylonic
454 4 Chemical Pulping Processes
0
2
4
6
8
10
0 200 400 600 800 1000 1200
Beech Aspen Eucalypt Birch Spruce
Viscosity [ml/g]
Xylan content [%]
Fig. 4.174 Xylan content as a function of viscosity of the
unbleached acid sulfite pulps made from beech, aspen, eucalyptus,
birch, and spruce (according to [14]). For cooking conditions,
see Tab. 4.62.
acid, and furfural. Furthermore, they also contain appreciable quantities of acetic
acid. At a given acid composition, the release of pentoses (C5-sugars) is clearly dependent
upon the H-factor and thus also on pulp viscosity. With prolonged cooking,
a slight reduction in the pentose content of the spent liquor is observed due
to further degradation reactions (Fig. 4.175), (see Scheme 4.30). The amount of
pentoses present in the spent liquor is clearly proportional to the xylan content in
the wood (see Tab. 4.61). Consequently, the highest yield of pentoses (xylose) is
obtained with birch as a wood raw material, followed by beech, eucalypt, aspen
and, at a clear distance, spruce.
The formation of furfural, derived from acid-catalyzed dehydration of pentoses,
depends on both the xylan content in the wood and the cooking conditions during
acid sulfite pulping (Fig. 4.176). The increase in furfural concentration with prolonged
cooking is more pronounced for hardwoods than for spruce, though this
may be related to the xylose concentration in the spent liquors.
The release of acetic acid occurs during the early stages of the cook. Thus, the
concentration of acetic acid in the spent liquor appears to be somewhat independent
of the cooking conditions, and is directly related to the acetyl content in the
respective wood species (Fig. 4.177).
4.3 Sulfite Chemical Pulping 455
0 200 400 600 800 1000 1200
0
30
60
90
120
150
Beech Aspen Eucalypt Birch Spruce
C5-sugars in SL [g/kg od wood]
Viscosity [ml/g]
Fig. 4.175 Pentoses (C5-sugars) in spent liquor (SL) as a
function of viscosity of the unbleached acid sulfite pulps
made from beech, aspen, eucalyptus, birch, and spruce
(according to [14]). For cooking conditions, see Tab. 4.62.
0 200 400 600 800 1000 1200
0
3
6
9
12
15
Beech Aspen Eucalypt Birch Spruce
Furfural in SL [g/kg od wood]
Viscosity [ml/g]
Fig. 4.176 Furfural formation in spent liquor (SL) as a function
of viscosity of the unbleached acid sulfite pulps made
from beech, aspen, eucalyptus, birch, and spruce (according
to [14]). For cooking conditions, see Tab. 4.62.
456 4 Chemical Pulping Processes
0 200 400 600 800 1000 1200
0
20
40
60
80
Beech Aspen Eucalypt Birch Spruce
Acetic Acid [g/kg od wood]
Viscosity [ml/g]
Fig. 4.177 Acetic acid content in spent liquor as a function of
viscosity of the unbleached acid sulfite pulps made from
beech, aspen, eucalyptus, birch, and spruce (according to
[14]). For cooking conditions, see Tab. 4.62.
Both furfural and acetic acid are steam-volatile compounds, and thus can be
recovered from the enriched evaporated condensates by liquid-liquid extraction,
followed by multi-stage distillation [32].
The acid sulfite spent liquors from softwoods predominantly contain hexoses,
as would be expected from the composition of their hemicelluloses. The prevailing
hexose in the spent liquor is mannose in a ratio to glucose significantly higher
(2.9:1) as compared to the composition in the wood (1.8:1). The higher xylan
retention in softwood pulp supports this observation. Among the hardwoods,
aspen releases the greatest amounts of hexoses in the spent liquor, mainly
because of the high mannose content. Figure 4.178 shows an increase in the
amount of hexoses with decreasing viscosity which can be substantiated by progressive
cellulose degradation. The traditional use of hexoses from softwood sulfite
spent liquors is that of fermentation to ethyl alcohol. Before fermentation, sulfur
dioxide must be removed from the liquor to prevent inhibition of the yeast
(Saccharomyces cerevisiae). Assuming the formation of 2 mol ethanol per mol
removed hexose, up to 4–5% of ethanol (based on o.d. wood) can be produced.
A complete material balance, including both the pulp and the spent liquor composition
of magnesium acid sulfite pulping of the selected five wood species, is
provided in Tab. 4.63. For better comparison, the yields of pulp and spent liquor
constituents are adjusted to cooking conditions appropriate for a pulp viscosity of
700 mL g–1.
4.3 Sulfite Chemical Pulping 457
458 4 Chemical Pulping Processes
Tab. 4.63 Material balance for a typical one-stage acid sulfite cook of five selected wood species (according to [14]).
Reaction conditions Pulp characterization Spent liquor characterization
Wood
species
TotSO2 Free SO2 [H+]*[HSO3] H-Factor Scr.
yield
Reject Kappa
number