- •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
Viscosity
[ml g–1]
before D
[ml g–1]
ClO2 NaOH H2O2 ClO2 NaOH H2O2 OXE
SW-Kraft D(EO)DED 29.5 1130 29.5 0.22 24.7 20.0 0.0 15.0 5.0 0.0 2942
SW-Kraft D(EOP)DED 29.5 1130 29.5 0.22 24.7 20.0 3.0 12.0 5.0 0.0 2896
SW-Kraft D(EO)DED 29.5 1130 29.5 0.28 31.4 24.0 0.0 12.0 5.0 0.0 3218
SW-Kraft D(EOP)DED 29.5 1130 29.5 0.28 31.4 20.0 3.0 9.5 5.0 0.0 3209
HW-Kraft D(EO)DED 16.5 1015 16.5 0.22 13.8 16.7 0.0 11.0 5.0 0.0 1839
HW-Kraft D(EOP)DED 16.5 1015 16.5 0.22 13.8 16.7 3.0 9.0 5.0 0.0 1867
HW-Kraft D(EO)DED 16.5 1015 16.5 0.26 16.3 17.2 0.0 9.0 5.0 0.0 1877
HW-Kraft D(EOP)DED 16.5 1015 16.5 0.26 16.3 17.2 3.0 8.0 5.0 0.0 1979
HW-Kraft ODEOPDD 14.6 33 1031 7.8 825 0.25 7.4 12.0 3.0 9.5 0.0 0.0 1428
HW-Kraft ODEOPDD 15.0 1090 9.5 865 0.22 7.9 13.6 3.0 6.1 0.0 0.0 1216
SW-Kraft ODEOPD 16.3 7.8 0.34 10.0 13.1 2.0 7.0 0.0 0.0 1375
SW-Kraft ODh/lEOPD 16.3 7.8 0.34 10.0 13.1 2.0 3.0 0.0 0.0 1079
SW-Kraft DEODD 17.0 17.0 0.25 16.2 21.0 0.0 5.0 0.0 0.0 1569
SW-Kraft Dh/lEODh/l 17.0 17.0 0.25 16.2 21.0 0.0 5.0 0.0 0.0 1569
HW-Kraft ODEDED 9.8 0.22 2.0 756
HW-Kraft OD*EDED 9.8 0.22 2.0 756
7.4 Chlorine Dioxide Bleaching 769
Tab. 7.35 Continued.
Pulp properties Reference
Pulp Sequence D(EO) pulp Final bleached pulp Chain scissions, x 104
[mol AGU–1]
kappa no. Dj/DClO2 brightn
% I SO
HexA
[mmol kg–1]
Viscosity
[mL g–1]
AOX
[kg odt–1]
overall after O
SW-Kraft D(EO)DED 4.4 1.02 89.6 1050 1.9 0.288 Lachapelle et al. [1]
SW-Kraft D(EOP)DED 3.4 1.06 90.8 1050 1.9 0.288 Lachapelle et al. [1]
SW-Kraft D(EO)DED 3.3 0.83 90.9 1050 2.0 0.288 Lachapelle et al. [1]
SW-Kraft D(EOP)DED 2.6 0.86 91.2 1050 2.0 0.288 Lachapelle et al. [1]
HW-Kraft D(EO)DED 4.0 0.9189.9 920 0.4 0.452 Lachapelle et al.[1]
HW-Kraft D(EOP)DED 2.4 1.02 90.8 920 0.4 0.452 Lachapelle et al. [1]
HW-Kraft D(EO)DED 2.4 0.86 90.3 920 0.4 0.452 Lachapelle et al. [1]
HW-Kraft D(EOP)DED 1.8 0.90 92.3 920 0.5 0.452 Lachapelle et al. [1]
HW-Kraft ODEOPDD 3.6 0.57 89.9 3.3 763 n.a. 1.559 0.466 Sixta [32]
HW-Kraft ODEOPDD 3.9 0.71 87.9 817 n.a. 1.375 0.315 Sixta [32]
SW-Kraft ODEOPD 87.5 Seger et al. [17]
SW-Kraft ODh/lEOPD 88.0 Seger et al. [17]
SW-Kraft DEODD 1.9 0.93 87.5 Seger et al. [17]
SW-Kraft Dh/lEODh/l 2.2 0.92 86.4 Seger et al. [17]
HW-Kraft ODEDED n.a. 89.4 975 0.41Ragnar & Torngren[13]
HW-Kraft OD*EDED n.a. 89.9 937 0.23 Ragnar & Torngren [13]
n.a. = not analyzed.
be lowered from 0.33 to 0.13 kg odt–1. It is of interest to note that applying the
modified pH profile in the D1 stage does not result in a higher total chlorine dioxide
demand to achieve a full brightness of about 90% ISO, despite a considerable
increase in the kappa number after the E stage as compared to a conventional
one-step chlorine dioxide bleach. Results with lignin-model studies have revealed
that the chlorination of nonphenolic lignin structures is highly affected by the pH
of the chlorine dioxide treatment. The extent of chlorination reactions decreases
considerably when the pH is increased beyond 5.5. These results led to the conclusion
that chlorine dioxide bleaching at low pH promotes delignification, while
chlorination diminishes at high pH. The AOX load in the DE-effluents can also
be reduced by eliminating washing between the D1 and extraction stages; this is
known as the Ultim-O process, and was proposed by Cook [19]. The approach
shows a similar reduction of AOX but, due to the avoidance of interstage washing,
the OX level in the pulp is much higher than compared to the two-step procedure.
The effectiveness of chlorine dioxide in delignification can be improved by an
addition of aldehydes [20]. The reaction of an aldehyde with the intermediate reaction
product chlorite regenerates active chlorine dioxide and increases the delignification
rate. The addition of formaldehyde or other aldehyde compounds
improves the kappa number reduction by 20–35%.
7.4.6
Technology of Chlorine Dioxide Bleaching
Andreas W. Krotscheck
The process flowsheet of a typical chlorine dioxide bleaching system is illustrated
schematically in Fig. 7.70. Medium-consistency pulp coming from the previous
bleaching stage drops into a standpipe and is mixed with chemicals for pH adjustment
as it enters the medium-consistency pump. Sulfuric acid or spent liquor
from the chlorine dioxide generation plant can be used to lower the pH, whilst
caustic soda is applied if the pH needs to be raised.
MC PUMP
HIGH-SHEAR
MIXER
REACTOR WASHING
ClO2
Pulp from
preceding
stage
Chemicals for
pH adjustment
Pulp to
next stage
Fig. 7.70 Process flowsheet of a typical chlorine dioxide bleaching system.
770 7Pulp Bleaching
The pump forwards the pulp suspension to a high-shear mixer which is charged
with the chlorine dioxide solution. Mixing chlorine dioxide into the pulp slurry is
rather unproblematic due to the dilute solution and long reaction time. Whilst in
older installations the chlorine dioxidewas added to the housing of theMCpump, the
current state of the art is high-shear mixing with moderate power dissipation.
The pulp suspension proceeds from the mixer to an atmospheric upflow reactor,
where the bleaching reaction takes place. Previously, chlorine dioxide bleaching
was sometimes carried out in upflow-downflow reactor combinations, where the
smaller upflow section was responsible for keeping the volatile chlorine dioxide in
solution under hydrostatic pressure, while the larger downflow section was used
to complete the reactions. A downflow reactor in the bleaching sequence has
some operational advantages because of its capability to buffer a certain pulp volume
during upsets. Depending on the feed requirements of the subsequent washing
equipment, the pulp slurry is discharged from the reactor either at low or medium
consistency.
Washing after a chlorine dioxide stage is usually carried out with single-stage
washing equipment, for example with a wash press, a single-stage Drum Displacer
™, an atmospheric diffuser, or a vacuum drum washer. The vent gases from
the chlorine dioxide stage equipment and tanks must be collected and scrubbed to
remove chlorine and chlorine dioxide. Scrubbing is often performed using an
alkaline bleaching liquor.
The preferred material of construction for the wetted parts in a chlorine dioxide
stage is titanium, but a high-molybdenum austenitic stainless steel may also be
appropriate. The towers are frequently tile-lined.
Further information regarding chlorine dioxide bleaching equipment, including
medium consistency pumps, mixers and atmospheric reactors is provided in Section
7.2, while details of pulp washing are collected in Chapter 5.
7.4.7
Formation of Organochlorine Compounds
The negative environmental impact associated with the use of elemental chlorine
is primarily related to the formation of chlorinated organic compounds. A large
variety of individual chlorinated compounds are formed during the chlorination
reactions, and the major part of these are released to the aqueous phase where
they are summarily detected as AOX (adsorbable organic compounds). Another
part of the chlorinated organic compounds remains in the bleached pulp; this is
denoted organic chlorine content, known as OCl or OX. The AOX fraction can be
classified into two categories of different molecular weight: (a) The high molecular
fraction (molecular weight >1000 Da), which constitutes about 80% of the
AOX and contains mainly hydrophilic and nonaromatic compounds; and (b) the
low molecular fraction, which consists of highly chlorinated compounds (e.g.,
polychlorinated phenolic compounds, etc.) that are potentially problematic and
toxic to aquatic organisms due to their ability to penetrate cell membranes. The
substitution of elemental chlorine with 100% chlorine dioxide during the first
7.4 Chlorine Dioxide Bleaching 771
bleaching stage (D0) significantly reduces AOX formation, and virtually eliminates
levels of polychlorinated phenols in the final effluents to below the limits of analytical
detection [21]. The generation of organically bound chlorine is linearly
related to the charge of active chlorine according to the following expression [22]:
AOX _ 0_1 __C _ D_5_ _82_
where AOX is adsorbable organic compounds (in kg odt–1), C is the amount of
chlorine (in kg odt–1), and D is the amount of chlorine dioxide (in kg, calculated as
active chlorine odt–1).
Equation (82), which is valid for softwood kraft pulps, indicates that chlorine
dioxide introduces only about one-fifth of the AOX formed during chlorine
bleaching. In the case of hardwood kraft pulps, less AOX is generated due to the
different chemical structure of hardwood lignin (syringyl units) as compared to
softwood lignin (guaiacyl units). The amount of AOX evolving from chlorine and
chlorine dioxide bleaching of hardwood kraft pulps can be estimated from Eq.
(82) by replacing the factor 0.1through 0.05 to 0.08, depending on the hardwood
species and reaction conditions.
Almost all of the chlorinated organic substances in the effluent of a multi-stage
ECF sequence comprising at least two D stages are formed in the D0 and E1 stages.
Kinetic studies have revealed that the generation of organic chlorine occurs very rapidly
[23], with the final amount of total chlorinated organic material (AOX+OX) being
produced within the first 10 min of reaction with chlorine dioxide (Fig. 7.71).
0 50 100 150
0,0
0,2
0,4
0,6
0,8
1,0
Kappa number
Organic Chlorine, kg/odt
Reaction time, min
OX in pulp AOX in Liquor
10
20
30
Kappa number
Fig. 7.71 Kinetics of organic chlorine formation (AOX and
OX) during D0 treatment of spruce kraft pulp, kappa number
28.7 (according to [23]). D0 conditions: 45 °C, 1% consistency,
kappa factor 0.22.
772 7Pulp Bleaching
The data in Fig. 7.71show that all the organic chlorine attached to the pulp
(OX) is formed within a very short time, while the increase in AOX in the bleaching
filtrate is predominantly due to increasing solubility of the chlorinated lignin
in the pulp throughout chlorine dioxide treatment. The same study revealed that
86% of the sum of AOX and OX originates from the reaction with hypochlorous
acid which is formed in situ through the step-wise reduction of chlorine dioxide
[see Eqs. (61), (63) and (64)]. Hypochlorous acid reacts with the chemical structures
present in lignin in a different way as compared to elemental chlorine,
which is created simply by shifting the pH below 2 [Eq. (66)]. In principle, the
extent of chlorination is lower for reactions with hypochlorous acid as compared
to those with elemental chlorine. As an example, hypochlorous acid reacts with
olefinic structures to form chlorohydrin, while chlorine converts them to dichlorinated
compounds [24]. The covalently bound chlorine is more easily eliminated
from chlorohydrins during subsequent alkaline extraction (by a SN reaction) than
from the dichlorinated structures derived from reactions with elemental chlorine.
Alkaline extraction following a D0 stage generally reduces the AOX and OX level,
depending on temperature and sodium hydroxide concentration. The elimination
of a washing step between D0 and E1 provides a reduction of 65% in the total level
of AOX in the effluents. This was demonstrated for an existing ECF bleaching
sequence processing E. globulus kraft pulp, kappa 13, where a DE pre-treatment
was replaced by a (DE) delignification unit, while keeping the final DED sequence
unchanged [25]. Unlike the Ultim-O process described above, the temperature
and pressure in the extraction stage were not altered. The sodium hydroxide in
the E1 stage was sufficient to neutralize the acidic carry-over in the effluent of the
D0 stage while maintaining the pH above 11.
Surprisingly, it was found that the AOX levels generated in a D0(EO)D(EP)D
sequence were higher for the oxygen-delignified softwood kraft pulps as compared
to the non-oxygen-delignified pulps when compared at the same kappa numbers
of the pulps entering the D0 stage [26]. The relationship between AOX and kappa
number for both types of pulp is shown graphically in Fig. 7.72.
The main difference between the unbleached and the oxygen-delignified pulps
is reflected in the higher content of HexA (4-deoxy-b-l-threo-hex-4-enopyranosyluronic
acid) in the latter, compared at the same kappa number, due to its resistance
towards oxygen delignification [27]. This indicates that the AOX formation
in the D0 stage is more dependent on the HexA content than on the kappa number,
as depicted in Fig. 7.73. HexA probably forms chlorinated dicarboxylic acids
in the presence of chlorine dioxide, which however is easily decomposed by
means of alkaline post-treatment [28].
The rule-of-thumb Eq. (82) is only valid within the conventional temperature
range used in D0 or D1 stages. The implementation of ECF bleaching in existing
bleach plants very typically was made by simply replacing chlorine with chlorine
dioxide. Some mills even today still operate a low-consistency D0 stage, because
the equipment was not modified. Similarly, the temperature was kept at the low
level required to run a C stage, or increased only moderately. Thus, typically D0
stages are operated between 45 °C and 70 °C (at best), and D1 or D2 stages at
7.4 Chlorine Dioxide Bleaching 773
0 10 20 30
0.0
0.5
1.0
1.5
2.0
SW-Kraft SW-Kraft-O
AOX, kg/odt
Kappa number
Fig. 7.72 AOX formation in the D0 stage as a function of the
kappa number of both oxygen-delignified and non-oxygendelignified
softwood kraft pulps (according to [26]).
0 10 20 30 40 50 60
0.0
0.5
1.0
1.5
2.0
SW-Kraft SW-Kraft-O
AOX, kg/odt
HexA content, μmol/g
Fig. 7.73 AOX formation in the D0 stage as a function of the
HexA content of both oxygen-delignified and non-oxygendelignified
softwood kraft pulps (according to [26]).
774 7Pulp Bleaching
70–80 °C. The application of a hot D0 stage, as described by Lachenal [29], alters
not only the bleaching results but also the effluent characteristics. Figure 7.74
compares the AOX load resulting from the treatment of a eucalyptus kraft pulp
with increasing amounts of chlorine dioxide in a hot D0 stage. An increase in the
chlorine dioxide, from 1% to 2% active chlorine, does not result in a doubling of
the AOX load. For comparison, the other technological alternative for a combination
of hot acid hydrolysis and chlorine dioxide delignification [30], hydrolysis for
110 min and addition of ClO2 (without intermediate washing), was tested. The
short retention of only 10 min at 90 °C results in a significantly higher AOX residual.
This is a clear indication of decomposition reactions taking place during the
2-h period at high temperature. Hydrolysis to inorganic chloride ions also occurs.
If such hydrolysis is conducted well ahead of the chlorine dioxide addition, and
the time following the addition is short, then degradation will not take place.
1,0 1,5 2,0
0,0
0,1
0,2
0,3
AOX formation [kg/odt]
Active Chlorine Charge [%]
D
hot
A
hot
/D
Fig. 7.74 Impact of active chlorine amount and addition
point in hot chlorine dioxide delignification on AOX load. Oxygen-
delignified eucalyptus kraft pulp, kappa 10. D0 at pH 3,
90 °C, 2 h; Ahot/D with 110 min acid hydrolysis at pH 3, 90 °C,
addition of ClO2 additional time 10 min.
It is therefore not surprising to see similarly lower AOX and OX values also in
high-temperature softwood pulp bleaching. The decrease does not require an
extreme residence time, as in this example 1h was applied to the D0 stage. The
effect is clearly the result of the very high temperature.
This impact is shown graphically in Figs. 7.7.5 and 7.76. In comparison to conventional
ECF bleaching [31], the amount of dissolved halogenated compounds
(AOX) is cut by more than half by increasing the temperature in the D0 and D1
stages. Similarly, the application of high temperature in other D stages reduces
the amount of halogenated compounds remaining in the pulp.
7.4 Chlorine Dioxide Bleaching 775
50.C+70.C 90.C+85.C
0.0
0.2
0.4
0.6
0.8
1.0
AOX formation [kg/odt]
Temperature in D stages [. C]
D
0
D
1
Fig. 7.75 Impact of high temperature on the
AOX load generated in bleaching oxygendelignified
(kappa 13.4) softwood kraft pulp.
Constant 3.35% active chlorine (kappa factor
0.25), 1 h and pH <3in D0, variable temperature
(50 °C or 90 °C); Eop with 1.8 %NaOH,
0.5% H2O2 and 0.4 MPa O2; D1 with 1% active
chlorine, 2 h, and 70 °C or 90 °C.
D1(70 .C) D1(90 .C) D1(70 .C) D1(90 .C)
60
90
120
150
180
D
0
at 90 .C
OX in pulp [g/odt]
D
0
at 50 .C
P D
2
(90 .C) D
2
(70 .C)
Fig. 7.76 Impact of the temperature in D stages on the residual
of halogenated compounds in pulp bleaching with the
sequences D0EopD1D2 or D0EopD1P. For conditions, see
Fig. 7.75; D2 with 0.5% active chlorine, P with 0.25% H2O2.
776 7Pulp Bleaching
When not only the D0 stage but also all other all D stages are operated at higher
than “normal” temperature, the residual of halogenated compounds remaining in
the pulp (“OX”) also decreases. When a final alkaline peroxide stage is added,
which results in additional saponification and extraction, the OX level of the pulp
reaches a level that would be accessible under conventional conditions only in
ECF “light” bleaching – that is, with a much lower input of active chlorine [15].
The explanation for the lower AOX and OX values is the reactivity of quinones
(see Section 7.4.4). A sequence with a final P stage is certainly more attractive for
reaching low OX values compared to the addition of sulfamic acid. Although the
addition of sulfamic acid similarly lowers the level of OX, a 25% higher charge of
chlorine dioxide is required [13].
7.5
Ozone Delignification
7.5.1