- •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
International
(Palmrose) definition
Total SO2 % od wood 17.5 17.5
Free SO2 % od wood 10.5 14.0
of total SO2 60 80
Combined SO2 % od wood 7.0 3.5
MgO % od wood 2.2
Liquor-to-wood ratio 3.5
Actual SO2 concentration
Total SO2 mol L–1 0.78
Free SO2 mol L–1 0.47
Bound SO2 (HSO3
–) mol L–1 0.31
a) Denoted also as true free and true combined SO2; this definition
may be used to convert both definitions into each other: % True
free SO2 = (% Free SO2 – % Comb. SO2)
% True Comb. SO2 = 2* % Comb. SO2.
396 4 Chemical Pulping Processes
The concentrations of the sulfur(IV) species in the aqueous cooking liquor are
defined through the following equilibria:
SO2 H2O _ H2SO3 SO2 _ H2O _ __H HSO_3 _159_
It has been shown that the major part of the sulfur dioxide in an aqueous solution
is not hydrated to sulfurous acid [6]. The hydrated and non-hydrated form of
the free SO2 are combined to express the first equilibrium constant Ka,1:
Ka_1 _
H _ _ HSO_3 __SO2 __H2SO3 _ _160_
The dissociation constant Ka,1 of combined SO2 decreases clearly with increasing
temperature, as seen in Tab. 4.53.
Tab. 4.53 Temperature-dependence of the first equilibrium
constant of free SO2 (according to [6]).
Temperature
[ °C]
pKa,1
25 1.8
70 2.3
100 2.6
110 2.8
120 3.0
130 3.1
140 3.3
150 3.5
Hydrogen sulfite ions are also in equilibrium with monosulfite ions and protons
according to the following expression:
HSO_3 _ H SO2_ 3 _161_
Hydrogen sulfite is a weak acid, and its equilibrium constant derived from
Eq. (159), and denoted as second equilibrium constant, Ka,2, is expressed as:
Ka_2 _
_H _ SO2_ 3 HSO_3 _ _ _162_
4.3 Sulfite Chemical Pulping 397
The pKa,2 can be approached by a value of about 7.0 at 25 °C. The change in ionization
of the hydrogen sulfite ion with temperature is unknown, and is assumed to
be insignificant. Consequently, pKa,2 is kept constant in the temperature range
prevailing in acid sulfite cooking.
The concentrations of the active cooking chemicals in a pure aqueous acid sulfite
cooking liquor, [H+], [HSO3
– ]and [SO3
2–], can be calculated by the following
simple equations:
The total SO2 concentration at any time and any pH is calculated as:
SO2_tot _ Ctot _ SO2 _ H2O _ HSO_3 SO2_ 3 _163_
The concentrations of [SO2.H2O], [HSO3
– ]and [SO3
2–]can be calculated accordingly:
SO2 _ H2O _ _Ctot _ HSO_3 SO2_ _ 3_ _164_
HSO_3 _ Ctot __SO2 _ H2O SO2_ _ 3_ _165_
SO2_ 3 _ Ctot _ SO2 _ H2O _ HSO_3 _ _ _166_
The pH-dependent concentrations of sulfur(IV) species can be calculated by using
the equilibrium equations:
Ka_1 _ Ctot _ HSO_3 SO2_ 3 _ _ _ __ H _ _ HSO_3 _167_
The hydrogen sulfite ion concentration can be calculated by rearranging Eq. (167):
HSO_3 _
Ka_1 _ Ctot _ SO2_ _ 3_ _Ka_1 _H _ _168_
A similar procedure can be applied to calculate the monosulfite ion concentration:
Ka_2 _ Ctot __SO2 _ H2O SO2_ _ _ 3____H _ SO2_ 3 _169_
SO2_ 3_
Ka_2 __Ctot __SO2 _ H2O _
_Ka_2 _H _ _170_
The course of pH as a function of the concentrations of the sulfur(IV) species in a
pure sulfite cooking liquor can be calculated by considering the equilibrium conditions
for the titration of a weak two-basic acid with strong alkali according to the
following expression:
398 4 Chemical Pulping Processes
__A_ _OH_ __H _AH _171_
Assuming the total concentration of the sum of the conjugated bases [A– ]and the
acid [AH]to be Ctot (in mol L–1), the acid–base equilibria can be calculated as:
_H _
Ka_1 _ Ctot
_Ka_1 _H _
Ka_2 _ Ctot
_Ka_2 _H _
10_14
_H _ C* _172_
where C* is the molar amount of the titrator base NaOH.
As an example, the course of pH of a pure aqueous sulfite solution with a total
SO2 concentration of 50 g L–1 (0.78 mol L–1) is calculated as a function of the free
SO2 concentration (Fig. 4.151). In the first case, the titration curve is calculated
according to Eq. (172), using sodium hydroxide as a titrator base. In the second
approach, the titration curve is calculated by means of ASPEN-PLUS simulation
software, using magnesium hydroxide as a titrator base. ASPEN-PLUS uses a
high-performance electrolyte module based on the NRTL model (nonrandom,
two-liquid) to calculate the thermodynamic properties of aqueous electrolyte systems
[9]. The model provides an accurate description of the nonideality of concentrated
aqueous solutions.
The titration curve estimated by means of Eq. (172) agrees well with that calculated
by ASPEN-PLUS in the pH range 1 to 4.5, until any of the free SO2 is quantitatively
converted to hydrogen sulfite ions. The course of pH beyond this point
1.0 0.5 0.0 -0.5 -1.0
0
2
4
6
8
10
Titrator base, NaOH: 25 .C 140 .C
Titrator base, Mg(OH)
2
25 .C
pH-value
Free SO
2
, mol/l
Fig. 4.151 Course of pH as a function of the
free SO2 concentration assuming an initial
total SO2 concentration of 0.78 mol L–1 at 25 °C
and 140 °C. Two calculation modes: (a) titration
curve calculated according to Eq. (170), using
NaOH as titrator base; (b) titration curve simulated
by means of ASPEN-PLUS using
Mg(OH)2 as titrator base.
4.3 Sulfite Chemical Pulping 399
develops differently for the two bases. The addition of Mg(OH)2 causes a rather
even slope of pH until the equilibrium is shifted to monosulfite ions, while the
addition of NaOH raises the pH more steeply.
The concentrations of ionic species of a sulfite cooking liquor are given as a
function of the liquor composition (e.g., the molar content of free SO2 and active
base) in Tab. 4.54.
Tab. 4.54 Concentrations of ionic species of sulfite cooking
liquor with increasing amount of active base concentration;
initial free S02 concentration 0.78 mol L–1; [H+]calculation
according to Eq. (172), [HSO3
– ]according to Eq. (168), [SO3
2– ]
according to Eq. (170) and [SO2-H2O]according to Eq. (164).
Free SO2
[moI L–1]
Base
[moI L–1]
[H+]
[moI L–1]
pH-Value [SO2.H2O]
[moI L–1]
[HSO3
– ]
[moI L–1]
[SO3
2– ]
[moI L–1]
[H+]*[HSO3
– ]
0.78 0.00 1.04·10–1 0.98 6.77·10–1 1.04·10–1 1.00·10–7 1.07·10–2
0.58 0.20 3.65·10–2 1.44 5.44·10–1 2.37·10–1 6.48·10–7 8.63·10–3
0.39 0.39 1.47·10–2 1.83 3.76·10–1 4.05·10–1 2.76·10–6 5.96·10–3
0.28 0.50 8.49·10–3 2.07 2.72·10–1 5.09·10–1 5.99·10–6 4.32·10–3
0.08 0.70 1.79·10–3 2.75 7.92·10–2 7.02·10–1 3.92·10–5 1.26·10–3
0.00 0.78 3.94·10–5 4.40 1.93·10–3 7.77·10–1 1.97·10–3 3.06·10–5
–0.02 0.80 3.97·10–6 5.40 1.91·10–4 7.62·10–1 1.92·10–2 3.02·10–6
–0.22 1.00 2.57·10–7 6.59 9.10·10–6 5.62·10–1 2.19·10–1 1.44·10–7
–0.42 1.20 8.64·10–8 7.06 1.97·10–6 3.62·10–1 4.19·10–1 3.13·10–8
–0.62 1.40 2.62·10–8 7.58 2.67·10–7 1.62·10–1 6.19·10–1 4.24·10–9
–0.74 1.52 5.68·10–9 8.25 1.51·10–8 4.20·10–2 7.39·10–1 2.39·10–10
–0.78 1.56 3.58·10–11 10.45 3.04·10–13 2.79·10–4 7.81·10–1 1.00·10–14
The relative concentrations of sulfur dioxide, hydrogen sulfite, and sulfite are
determined by the pH of the aqueous solution. Figure 4.152 shows that sulfur
dioxide is present predominantly as SO2.H2O and hydrogen sulfite ions at pH 1–
2, typical for acid sulfite cooking. With increasing pH, the proportion of hydrogen
sulfite ion increases significantly, and in the pH range characteristic for magnefite
cooking (3–5), sulfur dioxide is present almost exclusively in the form of hydrogen
sulfite ions. Above this pH level, the sulfite ions start to become the dominating
ionic species in the sulfite cooking liquor.
400 4 Chemical Pulping Processes
0 2 4 6 8 10
0
20
40
60
80
100
SO
2
.H
2
O HSO
3
- SO
3
2-
mol percentage
pH-value
Fig. 4.152 Relative molar percentage of SO2·H2O, hydrogen
sulfite and sulfite ions as a function of the pH at 25 °C. Data
based on information in Tab. 4.54.
Due to the decrease in the acid dissociation constant of hydrated sulfur dioxide,
Ka,1, with increasing temperature, the pH level of the acid sulfite cooking liquor is
shifted to higher values at cooking temperature (Fig. 4.151, Tab. 4.51). This must
be considered in acid calcium sulfite pulping by increasing the proportion of the
free sulfur dioxide concentration to avoid the formation of insoluble calcium sulfite.
The ionic product, [H+].[HSO3
– ], is said to be proportional to the rate of delignification
in the course of sulfite pulping [6]. According to Tab. 4.54, this ionic product
increases exponentially with decreasing pH, which is equal to an increase in
the free SO2 concentration. This result corresponds well with industrial experience.
Increasing the proportion of free SO2 in the cooking acid continuously
reduces the cooking time at given process conditions.
Moreover, the presence of free SO2 largely determines the vapor pressure of the
cooking acid at the prevailing temperature. Figure 4.153 illustrates the development
of the partial pressure of SO2 of a cooking acid with a total SO2 concentration
of 0.78 mol L–1 containing two different amounts of free SO2, 0.39 mol L–1
(50% of total) and 0.23 mol L–1 (30% of total), respectively, at varying temperature
levels.
The inter-relation of partial SO2 pressure, and free and total SO2 is exemplified
in Fig. 4.154 for two temperatures, 100 °C and 140 °C, the latter being typical for
the cooking phase.
4.3 Sulfite Chemical Pulping 401
0 50 100 150
0
2
4
6
0.78 mol/l ΣSO
2
/l; 0.39 mol/l free SO
2
0.78 mol/l ΣSO
2
/l; 0.23 mol/l free SO
2
partial pressure of SO
2
[bar]
Temperature [. C]
Fig. 4.153 Development of partial pressure of
SO2 of a cooking acid comprising two different
proportions of free SO2, 50% and 30% of total
SO2 concentration (0.78 mol L–1), as a function
of temperature. The equilibrium conditions
were simulated by means of ASPEN-PLUS [10]
based on the pioneering studies of Hagfeldt et
al. [11].
0,1 0,3 0,5 0,7
1
4
7
10
pH value
pSO2: 100 °C 140 °C
partial pressure of SO2 [bar]
Free SO2 [mol/l]
1
2
3
4
Total SO2: 0.78 mol/l
pH: 100 °C 140 °C
Fig. 4.154 Development of partial pressure of
SO2 and pH of the three-component system
magnesium oxide-sulfur dioxide-water as a
function of free SO2 concentration for two different
temperatures, 100 °C and 140 °C,
respectively, while keeping the total SO2 concentration
constant at 0.78 mol L–1. The equilibrium
conditions were simulated by means of
ASPEN-PLUS [10]based on the pioneering studies
of Hagfeldt et al. [11].
402 4 Chemical Pulping Processes
The total pressure of sulfite cooking acids containing large quantities of free
SO2 is largely determined by the partial pressures of SO2, water and, in the case of
hardwood pulping, also by considerable amounts of volatile carbonic acids (e.g.,
acetic acid, furfural, etc.) and carbon dioxide. Digester pressures are usually limited
to 8–10 bar, which means that gas must be released through the relief pressure
valve during the entire cooking phase. New cooking digesters are designed to
operate at higher pressures (>12 bar), which is an effective measure to further
reduce cooking time.
4.3.3