Effect of Totally Chlorine Free and Elemental Chlorine Free Sequences on Whole Stem Kenaf (Hibiscus cannabinus) Pulp Characteristics

Totally chlorine free (TCF) and elemental chlorine free (ECF) single and multistage sequences were used to bleach whole stem kenaf pulp. The results indicated that in contrast to unbleached kraft wood pulps, kraft kenaf pulps can be easily bleached to a brightness of 91.4% using a four-stage TCF [Q₁(PO)Q₂P] bleaching sequence. The ECF bleaching pulps had slightly higher selectivity and yield than those of the TCF bleached pulps. The strength properties of the TCF [Q₁(PO)Q₂P] and ECF (D₁ED₂EP) bleached pulps were comparable, with the exception of tear index and tensile index, which were slightly higher and lower for TCF pulps, respectively.     

Totally chlorine‐free bleaching of Acetosolv pulps: a clean approach to dissolving pulp manufacture

Eucalyptus globulus wood samples were delignified in media containing concentrated acetic acid, water and hydrochloric acid (Acetosolv process) under optimized conditions, and the pulps were subjected to totally chlorine‐free (TCF) bleaching. Alkaline extractions, oxygen delignification, ozone treatment, enzymatic xylan removal and hydrogen peroxide oxidation in alkaline media were investigated as individual steps in selected bleaching sequences. Under the best conditions, fully bleached pulps with favourable characteristics for dissolving pulp manufacture were obtained. © 2001 Society of Chemical Industry     

Effect of bleaching without chlorine on the change in the optical properties of pulp in grinding

Yellowing occurs in grinding for almost all kinds of pulp, but the causes can be due to different mechanisms. One cause is an increase in transparency and a decrease in the specific light scattering coefficient due to this, which increases the intensity of the transmitted light beam and correspondingly decreases the intensity of the reflected light beam and the reflection factor. The second cause is disintegration during grinding of dark, poorly delignified particles (wood residues, shavings, fibril aggregates) not completely removed during sorting. Although some TCF pulp yellows much more strongly during grinding than ECF pulp, it is still early to draw any conclusions concerning the best characteristics in grinding ECF pulp. Much depends on the bleaching reagents, and the type of alkali base used is especially important, which is characteristic of TCF pulps. Pulps bleached with caustic soda yellows less on grinding than pulp bleached with magnesium hydroxide. In the last case, a high residual lignin content was also observed. For the same kappa number, pulps treated with ozone yellow more on grinding than pulps after oxygen-alkali delignification. The kappa number cannot be a good indicator of the degree of delignification in treatment with ozone, since this process cannot remove lignin-containing wood residues and shavings. The behavior of pulp in grinding in this case better characterizes the effectiveness of bleaching.     

Effect of Eucalypt Pulp Pretreatment with Hot Acid Hydrolysis on (aZe)DP and (aZe)(EP)P Bleaching Performance

The effect of pulp pretreatment with hot acid hydrolysis on high consistency ozone bleaching was evaluated. An experimental plan was set up involving the full optimization of the A-stage and its application in Elemental Chlorine Free–ECF–[A/(aZe)DP and A(aZe)DP] and Total Chlorine Free–TCF–[A/(aZe)(EP)P and A(aZe)(EP)P] sequences for eucalypt kraft pulp bleaching. The A-stage removed a significant amount of lignin and HexA from the pulp, and the subsequent Z-stage remained efficient after completion of the A-stage. The chemical savings caused by the A-stage were significant (～7 kg ClO₂/adt). The optimum conditions for the A-stage were pH 3.0, 90°C for 120 min, and 10% consistency. The strength properties of pulps bleached with the (aZe)DP (reference) and A/(aZe)DP ECF sequences were similar, but the TCF sequence A/(aZe)(EP)P delivered slightly lower strength properties than the ECF sequences. Fiber peeling studies indicated that the HexA present in the kraft pulp is not concentrated on the fiber surface, as previously thought.     

GC/MS characterization of effluents front the ozone bleaching of eucalypt kraft pulps

Concerns regarding the possible environmental effects of organochlorine by‐products from bleaching of pulp with chlorine‐based compounds have led to the pulp and paper industry developing new bleaching sequences. Ozone, oxygen and hydrogen peroxide are the main reagents in these Totally Chlorine Free (TCF) bleaching processes.

In this study, eucalypt kraft pulps from a variety of Australian wood sources were subjected to bleaching sequences comprising oxygen, ozone and hydrogen peroxide/alkali extraction stages. The aqueous liquid effluents from each stage were analyzed by GC/MS for aldehydes, ketones, alcohols, carboxylic acids and other by‐products. Pentafluorobenzyl oxime derivatives of the aldehydes and ketones were analyzed by electron impact GC/MS. The major carbonyl compounds detected were formaldehyde, glyoxal, dimethylglyoxal and acetone. An homologous series of n‐aldehydes corresponding to cleavage of ω‐3, 6, 9 and 12 unsaturated fatty acids also was detected. Aromatic aldehydes were identified in the oxygen stage and high consistency ozone stages, but not in any medium consistency ozone or post‐ozone bleach stages. In all stages a series of saturated alkyl carboxylic acids from formic to octacosanoic acid was detected. Formic and acetic acids were present in the highest yield. Only trace quantities of unsaturated fatty acids were detected. Details of these and other compounds detected are discussed.     

Inorganic Reactions in Chlorine Dioxide Bleaching of Softwood Kraft Pulp

Abstract

A softwood kraft pulp (27 kappa) was bleached with chlorine dioxide to various end pH values. The formation of chlorite, chlorate, and chloride was measured to quantify the amount of chlorine dioxide wasted as a function of pH during a D_o (pre‐bleaching) stage. Chlorate formation increased with a decrease in final pH. Conversely, residual chlorite increased with an increase in the final pH. After 120 min of bleaching the total residual chlorite and chlorate showed that no substantial increase in residual oxidant occurs when bleaching to an end pH below 3.4. As a result, the brightness and permanganate numbers for low pH chlorine dioxide bleached pulps did not differ when bleaching to an end pH between 3.4 and 1.8. However, decreasing the pH below 3.4 did result in increased organic chloride formation. The results are contrary to previous studies where the maximum bleaching efficiency for a D₁ stage was reported to occur when the end pH was between 3 and 4.     

Effect of xylanase on ozone bleaching kinetics and properties of Eucalyptus kraft pulp

Environmental pressure has led the pulp and paper industry to develop new technologies in order to reduce or suppress the presence of various pollutants in effluents from bleaching plants. One of the choices for this purpose is enzyme‐based biotechnology. This study deals with the effect of using a xylanase‐based enzymatic pretreatment, in a TCF (Totally Chlorine Free) sequence, on the properties of the resulting paper pulps. The hexenuronic acid content in the pulp and the physical properties of the paper were also studied. The performance of the xylanase was analysed through kinetic studies on ozone bleaching. The enzymatic pretreatment results in easier bleaching and delignification of the pulp, causing a bleach‐boosting effect. The decreased consumption of reagent is related to a decreased content of hexenuronic groups. The physical properties of the treated pulp are similar to those of untreated pulps. Cellulose degradation, delignification and chromophores' removal show first‐order kinetics. Enzyme pretreatment leads to differences between the kinetic constants of cellulose degradation and chromophores' removal, due to an increased accessibility to bleaching agents. The xylanase treatment leads to a lower floor kappa number (IK_∞) during the ozone stage. Copyright © 2003 Society of Chemical Industry     

Formic Acid-Peroxyformic Acid Pulping of Fagus sylvatica

Abstract

Beech (Fagus sylvatica) wood samples were subjected to two-stage treatments following the philosophy of the Milox process. By means of incomplete, second-order, factorial designs, the effects of selected operational variables on the composition and on the technical properties of pulps were assessed for optimization purposes. Under the best conditions assayed, a pulp with 5.5% lignin, 86.3% cellulose and 4.3% xylan was obtained at 46.6% pulp yield. The selected pulp showed good technical properties (kappa number = 25, SCAN viscosity higher than 1000 mL/g, R-10 test for alkaline resistance = 88.9%, R-18 test for alkaline resistance = 91.8%), showing potentiality to be used as feedstock for dissolving pulp production after TCF bleaching.     

Integrating laccase–mediator treatment into an industrial‐type sequence for totally chlorine‐free bleaching of eucalypt kraft pulp

Enzymatic delignification using the high‐redox potential thermostable laccase from the fungus Pycnoporus cinnabarinus and a chemical mediator (1‐hydroxybenzotriazole) was investigated to improve totally chlorine‐free (TCF) bleaching of Eucalyptus globulus kraft pulps. Different points of incorporation of the enzyme treatment into an industrial‐type bleaching sequence (consisting of double oxygen, chelation and peroxide stages) were investigated in pressurized laboratory reactors. The best final pulp properties were obtained using an O? O? L? Q? PoP sequence, where a laccase–mediator stage (L) was incorporated between double oxygen and chelation. The worse results, when the enzymatic and chelation treatments were combined in a unique stage, seemed related to partial inhibition of laccase‐mediator activity by the chelator. The new TCF sequence including the laccase stage permitted to improve eucalypt pulp delignification to values around kappa 5 (hexenuronic acid contribution over 50%) compared to kappa 7 using only TCF chemical reagents. In a similar way, the final brightness obtained, over 91% ISO, was 3–4 points higher than that obtained in the chemical sequences. Although technical and economic issues are to be solved, the results obtained show the feasibility of integrating a laccase–mediator treatment into a TCF sequence for bleaching eucalypt kraft pulp. Copyright © 2006 Society of Chemical Industry     

Optimized Catalytic Bleaching Sequences for Eucalyptus Kraft Pulp

Contemporary multi-stage bleaching processes partially remove residual lignin and hexenuronic acid from cellulosic pulps. The reactions in the steps could be faster and consume smaller amounts of chemicals. Catalytic bleaching (H_cat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyl triethylenediamine (CM-DABCO), is a new discovery that has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g. through reducing the reaction time of the bleaching processes. The objective of this study was to clarify if new kraft pulp bleaching sequences with initial stage of chlorine dioxide (ClO₂; D) and an intermediate stage of H_cat could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include D₀E_(OP)H_cat(Q)P and H_catZ/DP, which attained a final brightness of 88 and 89% ISO, respectively. H_catZ/DP showed to be the best sequence for the catalytic bleaching of eucalyptus kraft pulps. This study may open new doors to future bleaching of cellulose pulps with fewer towers and decreased use of chemicals.     

Separate Bleaching of Pulp Fractions Enriched in Earlywood and Latewood Fibers

Abstract

Unbleached softwood kraft pulp was fractionated in hydrocyclones into a fine fraction, enriched in earlywood fibers, and a coarse fraction, enriched in latewood fibers. The response to individual bleaching chemicals and the bleachability in bleaching sequences of the pulp fractions was studied.

The light absorption coefficient, light scattering coeffient, and brightness were higher in the unbleached fine fraction than in the coarse fraction. Hydrogen peroxide managed to reduce the light absorption coefficient of the earlywood enriched fine fraction more efficiently than that of the latewood enriched fraction.

In the TCF‐sequence the light absorption coefficient of the fine fraction was reduced to the level of the coarse fraction at a given consumption of bleaching chemicals. In the ECF‐sequence the difference in light absorption coefficient remained between the fractions. At a given consumption of bleaching chemicals, the fine fraction had higher brightness than the coarse fraction, 2%‐ and 1%‐units on the ISO‐scale in the TCF and ECF bleaching sequence, respectively.     

制浆漂白技术新进展

讨论了制浆漂白技术新进展,包括：深度脱木素蒸煮、氧脱木素、ECF无元素氯漂白）、TCF（全无氟漂白）、生物漂白。     

Eucalyptus globulus kraft process modifications: Effect on pulping and bleaching performance and papermaking properties of bleached pulps

BACKGROUND: Increasing the yield of the wood pulping process allows the reduction of specific wood costs. Process modifications with a great impact on pulp yield are the profiling of chemical charges and addition of anthraquinone (AQ). The aim of the present work is to investigate the influence of effective alkali (EA) profiling and addition of anthraquinone on E. globulus kraft pulping performance. The impact of such process modifications on the ECF bleaching process and on the papermaking properties of the resulting bleached pulps is also evaluated. RESULTS: An EA profiling cook may lead to a pulp yield gain, which is more significant as the total EA charge used in the kraft cook increases. AQ addition to kraft pulping leads to a significant yield increase. The ClO₂ charge required to fully bleach the pulps is lower for EA profiling and higher for kraft + AQ unbleached pulps. Bleached AQ pulp presents a high beatability due to high pulp xylan retention. CONCLUSION: A low total EA charge is the key parameter for high polysaccharide retention on pulp. AQ addition constitutes a feasible strategy to increase pulp yield. Bleaching performance and papermaking properties of pulps produced with the three different methods may be affected by the kraft pulping modifications. Copyright © 2008 Society of Chemical Industry     

The final bleaching of eucalypt kraft pulps with hydrogen peroxide: relationship with industrial ECF bleaching history and cellulose degradation

BACKGROUND: The process of chemical pulp bleaching is based for the most part in chlorine dioxide within elemental chlorine free (ECF) technologies. The use of greener alternatives such as bleaching with hydrogen peroxide (P stage) is not widely used owing to selectivity concerns related to transition metal‐catalyzed decomposition reactions. Even at the final stage where peroxide is recognized to boost brightness and improve the brightness stability of the bleached pulp, cellulose degradation often overcomes these advantages. This paper presents the results of studies intended to optimize final peroxide bleaching performance considering two standard ECF industrial bleaching sequences: the conventional DED and the ECF‐light OQ(PO)D (stages name: D—chlorine dioxide; E—alkaline extraction; O—oxygen; Q—chelation, (PO)—hydrogen peroxide pressurized with oxygen). RESULTS: The addition of sodium diethylenetriaminepentaacetate (DTPA) was the most effective option in terms of DED pulp bleachability and selectivity with hydrogen peroxide, as well as in terms of brightness reversion. As regards the OQ(PO)D pulp, a blend of DTPA and magnesium was the most beneficial in those properties. CONCLUSIONS: The choice of the best hydrogen peroxide stabilizer, among the different tested combinations of magnesium and chelants (EDTA and DTPA) studied, in terms of pulp bleachability, bleaching selectivity and brightness reversion is dependent on the impact of the previous bleaching stages on metallic nature and content. The pulp Mg/(Fe + Cu) ratio was highlighted as a process parameter controlling cellulose degradation in peroxide bleaching. Copyright © 2010 Society of Chemical Industry     

木聚糖酶NY—111对桉木KP浆漂白的研究

探讨了木浆糖酶ＮＹ－１１１用于桉木ＫＰ浆漂白预处理的最佳工艺条件及木聚糖酶预处理对桉木ＫＰ浆ＣＥＨ三段漂的影响。结果表明,用于漂白预处理的最佳工艺条件为酶 ５ＩＵ／ｇ,时间为２ｈ,对ＣＥＨ三段漂的影响为：与常规法１０％用氯量相比,达到相近白度且得率相近时,采用木聚糖酶预处理,可减少约５０％的用氯量、而强度未下降。     

Evolution of ozone for the bleaching of paper pulps

Although ozone has been studied seriously as a substitute for chlorine in the bleaching of pulp for paper making since 1949, it has only been since 1992 that ozone has begun to reach its full‐scale commercial potential. In this evolution, ozone has been aided immeasurably by environmental pressures to diminish the discharge of halogenated organics in pulp mill wastewaters. Thanks to the incorporation of ozonation into bleach processes, not only is the creation of halogenated organics minimized (and even eliminated in some cases), but this allows some of the processing liquors to be recovered and volumes of bleach plant effluents to be reduced. As a consequence, this not only decreases the volume of wastewater being discharged to the receiving water bodies, but also increases the potential for the Totally Effluent‐Free (TEF) bleached pulp mill to become a future reality.

Ozone's evolution in this rapidly growing industry is traced, and some characteristics of the 14 full‐scale pulp mills currently using and five additional planning to use ozone for pulp bleaching in various parts of the world will be described.     

Extractive Profiles in the Production of Sulfite Dissolving Pulp from Eucalyptus Globulus WOOD

The profile of major families of extractives soluble in acetone and dichloromethane during the production of acid sulfite dissolving pulp from Eucalyptus globulus wood was assessed. Nearly 85% of total extractives were removed from wood during pulping and nearly 11% in the course of E-O-P pulp bleaching and secondary pulp screening. Unlike extractives of polyphenolic origin that were almost completely removed after the alkaline extraction stage (E), fatty acids were the main retained component in fully bleached pulp followed by sterols and fatty alcohols. Throughout the bleaching steps, the profiles of extractives were not necessarily decreasing and depended on their reactions with bleaching reagents and the presence of auxiliary chemicals (e.g. antifoams). In this context, the content of fatty acids and fatty alcohols was mostly vulnerable. It has been suggested that Fock reactivity of dissolving pulps is unaffected by extractives at concentrations up to 0.3%.     

Lipophilic Extractives in Eucalyptus globulus Kraft Pulps. Behavior during ECF Bleaching

Abstract

The composition of E. globulus kraft pulp lipophilic extractives and their behaviour during an ECF (DEDED) bleaching sequence were investigated. Sterols; fatty acids, including several α‐ and ω‐hydroxyfatty acids; and long‐chain aliphatic alcohols are the major lipophilic extractives of the unbleached pulp. During the bleaching, about 80% of the aliphatic extractives are removed from pulp (ca. 70% of the sterols, 70% of the fatty acids, and 90% of the long‐chain aliphatic alcohols). The decrease of sterols is mainly due to the degradation of β‐sitosterol by chlorine dioxide, while the decrease of fatty acids and alcohols is essentially assigned to their extraction and elimination with the alkaline filtrates. The major chemical transformations in pulp extractives composition and structure occur in the last bleaching stages.     

Mechanistic Differences Between Kraft and Soda/AQ Pulping. Part 1: Results from Wood Chips and Pulps

Abstract

Soda pulping catalyzed by anthraquinone (AQ) or 2-methylanthraquinone (MAQ) can produce hardwood chemical pulps similar to kraft pulps in all respect but for bleachability. Results accumulated in our laboratory suggest that the residual lignin in pulps from anthraquinone catalyzed processes is less reactive toward bleaching chemicals than that in kraft pulps. Analyses of pulps by periodate and permanganate oxidations suggest that the residual lignin from the non-sulfur processes contained more condensed structures than kraft residual lignin. The low reactivity of these structures is believed to be responsible for the lower brightness of bleached soda-AQ (SAQ) pulps. Pulping and bleaching trials with hardwood chips demonstrated that shortening of the cooking time and/or increasing the alkalinity is one strategy for improving bleachability of SAQ pulps. When sugar maple (Acer saccharum) chips were SAQ cooked for 1.0 and 2.0 h at 165°C, the higher kappa number pulp produced after 1.0 h of cooking bleached to a significantly higher brightness with a small increase in the chlorine dioxide application.     

TCF BLEACHED PULPS FROM MISCANTHUS SINENSIS BY THE IMPREGNATION RAPID STEAM PULPING (IRSP) PROCESS

ABSTRACT

The production of bleached cellulose pulps from elephant grass (Miscanthus sinensis) via a two-stage soda pulping process and a TCF bleaching sequence is evaluated in this work. The impregnation rapid steam pulping process (IRSP) involves impregnating of the lignocellulosic material with the pulping liquor, withdrawing the excess liquor and rapidly steaming the impregnated material at 180–200°C for a short time. In this paper the process variables and their effect on the kappa number, yield and viscosity of the unbleached pulps are discussed. Bleaching by an ozone-based TCF sequence was tested, and the papermaking properties of the bleached pulp were determined. A kappa number of 19 was obtained by impregnating at an alkali charge of 30 + 0.1% anthraquinone carboxylic acid (AQCA) and pulping at 180°C for only 15 min. Kappa was reduced to 16 by extending pulping time to 26 min. The alkali consumption during impregnation and pulping was 10.2 g NaOH/100 g of dry Miscanthus. Screened pulp yield, viscosity and brightness for this pulp were 54.6%, 913 mL/g and 37.3%, respectively. After bleaching, the pulp had an ISO brightness of 87.4% and a viscosity of 700 mL/g. Refining in a PFI mill provided optimal strength properties of the bleached pulp at 4500 revolutions (71°SR): breaking length 7.2 km, tensile index 72 N m/g, and burst index 4.3 kN/g. Tear index was 7.9 mN m²/g at this degree of refining.