SCIENTIFIC ARTICLES

Biorefinery & Pulping

Modeling of alkaline extraction chemistry and kinetics of softwood kraft pulp.

ABSTRACT A comprehensive model for alkaline extraction (E) of chlorine dioxide delignified (D0) softwood kraft pulp (KP) is presented. The dynamics of the process is modeled by taking into account both irreversible and reversible chemical reactions and gas-liquid and liquid-liquid mass transfer. Equations linking molecular-scale composition (amounts of monomeric lignin and carbohydrate structures) and general engineering parameters [κ number (KN),…

Determination of the contribution of penetration, diffusion and alkali consumption in the impregnation of Eucalyptus grandis chips.

ABSTRACT The influence of impregnation conditions on the phenomena involved in the impregnation of Eucalyptus grandis chips was studied with the aid of a new impregnation method. When pre-steaming was used, 30 minutes of penetration time was sufficient to achieve the final degree of penetration (over 95%) with white and black liquor. An impregnation time of 15 minutes was found…

Determination of phenomena involved in impregnation of softwood chips. Part 1. Method for calculating the true penetration degree.

ABSTRACT In earlier studies the degree of penetration was calculated with a method which gave a penetration degree of over 100%, if mill liquors were used, because the method ignored the diffusion of cooking chemicals and dissolution of wood material. In this paper, a new experimental research method is presented, which allows the penetration of mill liquors to be examined…

Determination of phenomena involved in impregnation of softwood chips. Part 2: alkali uptake, alkali consumption and impregnation yield.

ABSTRACT The influence of impregnation conditions on the phenomena involved in impregnation was studied with the aid of a new impregnation method. The method was found to be good enough for scientific research purposes and useful for gaining new knowledge of the alkali uptake, alkali consumption and dissolution of wood material during impregnation. An impregnation time of slightly over 15…

The Effect of Process Variables in Chlorine Dioxide Prebleaching of Birch Kraft Pulp. Part 1. Inorganic Chlorine Compounds, Kappa Number, Lignin, and Hexenuronic Acid Content.

ABSTRACT This study investigated the effects of temperature, chlorine dioxide dosage, and filtrate circulation on various filtrate and pulp properties in chlorine dioxide prebleaching of birch kraft pulp. Also the effect of a preceding A-stage was examined. Kappa number, delignification, and hexenuronic acid removal were unaffected by the used dilution media and temperature. Increasing ClO2 charge resulted in a lower…

Towards complete impregnation of wood chips with aqueous solutions. Part I. A retrospective and critical evaluation of the penetration process.

ABSTRACT This paper evaluates the process of liquid penetration into wood chips from the retrospective viewpoint of industrial development and research and provides a summary of currently available knowledge in this area. During the past few decades, researchers have been dealing mainly with pulping chemistry and the back-end of pulping processes, while less attention has been paid to the front-end…

Penetration of water into industrial softwood chips – influence of physical properties.

ABSTRACT In earlier studies, the fundamentals of the liquor penetration process in the case of hand made, homogenous, identically shaped wooden blocks have been studied. However, the efficiency of liquor penetration into real industrial chips may differ from the efficiency of penetration into ideal handmade chips. In this paper, impregnation experiments with three industrial softwood chip grades including sawmill chips,…

Penetration of water and black liquor into overthick and treated wood chips.

ABSTRACT In this paper, the penetration of water and black liquor into overthick and pre-treated overthick chips (cracked and re-chipped according to thickness) was studied with a laboratory impregnator to investigate ways to improve penetration. Overthick chips were divided in three categories: knot-containing chips, chips without knots and original overthick chips. The results of the penetration experiments were evaluated in…

Solving soap and turpentine related process problems in softwood draft mills

Abstract Effective separation of soap and turpentine is an important, but mill-specific aspect, regarding the entire softwood kraft process performance. This paper describes a systematic approach to evaluate and solve various extractives-related process problems. In a mill “audit”, the soap and extractives potential of the mill’s wood raw material is first estimated, the key process streams are tested and the…

Towards complete impregnation of wood chips with aqueous solutions. Part 5: improving uniformity of kraft displacement batch pulping.

ABSTRACT Pulping uniformity is critical for improving the performances of cooking and downstream operations such as bleaching and papermaking. In spite of certain success of recent modifications of batch and continuous kraft cooking systems, there is still a lot of room for improving the contemporary cooking systems in order to address problem of heterogeneous pulping. Incomplete penetration and inadequate diffusion…

Towards complete impregnation of wood chips – new research enables effective processes.

ABSTRACT The important role of impregnation prior to chemical pulping has been long recognized qualitatively but not fully realized quantitatively. Cost effective production of uniform, high quality pulp can only be achieved by efficient mass transfer of pulping chemicals that must start with complete impregnation of wood chips. The present paper describes the main results of an in-depth research project…

The washing efficiency of digester displacement: new aspects based on laboratory studies and improved calculation procedures.

ABSTRACT Displacement batch cooking is nowadays a common practice in the production of kraft pulp. The cook is terminated by a cool filtrate displacement, in which the temperature of the digester is brought down. The terminal displacement is the first washing stage in the pulp mill. The displacement operation is widely practiced, but knowledge of the washing effect of the…

Towards complete impregnation of wood chips with aqueous solutions. Part 4. Effects of front-end modifications in displacement batch kraft pulping.

ABSTRACT The front-end of kraft cooking, i.e. steaming, impregnation and heating, controls the cooking performance in terms of mass transfer, delignification and cooking uniformity. Therefore, it is of vital importance to understand the process mechanisms and optimise the front-end process conditions. This article discusses the effect of applying chip presteaming and higher pressure at the front-end of kraft displacement batch…

Efficiency of chip presteaming – result of heating and air escape processes.

SUMMARY Efficient removal of air from the wood chips prior to impregnation with cooking liquor is important for achieving pulping uniformity and improving the overall digester performance. Because of its effectiveness, relative simplicity and other advantages, steaming of wood chips became a primary process in pulp industry to fulfil this task. In the present article the process of chip presteaming…

Towards complete impregnation of wood chips with aqueous solutions. Part 2. Studies on water penetration into softwood chips.

ABSTRACT Importance of the chip impregnation stage is widely recognised in chemical pulping processes. However, there is limited amount of direct data on mass transfer during the impregnation stage. Most methods used for studying the liquid penetration process were based on indirect approaches. A new laboratory impregnator with a special weight sensor was developed, which allowed the direct measurements of…

Towards complete impregnation of wood chips with aqueous solutions. Part 3. Black liquor penetration into pine chips.

ABSTRACT Presteaming of chip and applied pressure greatly influence penetration of black liquor into pine chips. Complete penetration of sapwood chips can be reached just by applying extra pressure. To achieve a high degree of penetration of the heartwood chips, air present within the wood capillaries has to be removed by presteaming. Efficient liquor penetration achieved by optimising conditions at…

Softwood fiber damage – a newly discovered enigma in modern kraft fiber lines.

ABSTRACT Studies of pulp strength delivery have shown that cooking is the most significant step causing strength losses in softwood pulp. In the early 1990s it was demonstrated that different cooking processes resulted in different strength delivery and that displacement kraft batch cooking systems resulted in a pulp strength which comes very close to the strength of the laboratory reference…

Behavior of pine wood material during displacement kraft batch cooking.

ABSTRACT Pine wood (Pinus sylvestris) was delignified using a modern displacement kraft cooking method. A series of laboratory-scale cooks (stop-cooks) was carried out to different cooking degrees representing i) the end points of warm black liquor impregnation (temperature 80°C, total yield 93.3%) and hot black liquor pretreatment (temperature 155°C, total yield 77.5%) and ii) varying chlorine numbers (1.8-7.0) in the…

Effects of softwood morphology and chip thickness on pulping with a displacement kraft batch process.

ABSTRACT This study examines the effect of softwood raw-material properties on pulp quality. Logs of Scots pine (Pinus sylvestris), Norway spruce (Picea abies), and loblolly pine (Pinus taeda) were the raw materials. Wood from Scots pine and Norway spruce was further classified by age as (a) pulpwood (mature wood and older thinnings) or (b) young wood (first thinnings and top…

Relations between cooking conditions, pulp quality and bleachability as studied using a new superbatch experimental cooking system.

ABSTRACT Cooking, oxygen delignification, and ECF bleaching characteristics of Scandinavian pine were studied using a recently implemented lab. scale displacement cooking system.  Cooking with white liquor was varied over a wide range in order to produce pulps of varying delignification degrees and yields with const. impregnation and hot black liquor treatment.  The pulps were then oxygen delignified and bleached with a D(EOP)​DD sequence, again varying conditions in order to evaluate delignification and brightness…

Chip thickness vs. kraft pulping performance: experiments by multiple hanging baskets in batch digesters.

ABSTRACT Differently screened chip samples were placed in baskets and were cooked inside industrial batch digesters.  These basket pulps were analyzed with regard to yield, delignification degree, rejects, and pulp strength.  Thickness screening was shown to be advantageous to conventional batch cooking and to full displacement cooking.  In both methods, the rejects could be cut in half by using thickness– ​screened chips.  Moreover, the SuperBatch cooking process, a modified full…

Substituent effects on carbon-13 chemical shifts of aromatic carbons in β-O-4 and β-5 type lignin model compounds.

ABSTRACT Substituent effects on the chemical shifts of aromatic carbons in lignin model compounds have been elucidated from C NMR spectra of guaiacyl and syringyl type monomerio and β-O-4 model compounds and guaiacyl type β-5 model compounds. Evaluation of the observed values of substituent chemical shift (SCS) for the aromatic carbons leads to elucidation of a generalized SCS additivity rule,…

Separation of sulfite spent liquor components by ion exclusion chromatography

ABSTRACT Small and pilot plant scale expts. showed that ion-​exclusion chromatog. with Amberlite IR 140 columns is an efficient technique for the sepn. of spent sulfite liquor (SSL) components into reasonably pure and sugar-​free lignosulfonate and tech. grade sugar fractions.  The use of strongly acidic cation exchanger in the same ionic form as the SSL obviated the need for regeneration between samples, which are displaced with H2O.

Bleaching

A Model for Chlorine Dioxide Delignification of Chemical Pulp.

ABSTRACT A phenomenon based model for chlorine dioxide delignification of chemical pulp is introduced. The pulp suspension environment is modeled using the concept of two liquid phases, one inside and the other external to the fiber wall. Physico-chemical processes taking place during delignification are implemented with thermodynamic, mass transfer and reaction kinetic models. A broad library of chemical reactions is…

Specific Permeability of Wood to Water. Part 1: Longitudinal Specific Permeability of Steamed, Impregnated, and Kraft-Cooked Wood.

ABSTRACT Two apparatuses for measuring the specific permeability of wood specimens are presented. The developed method was used to measure specific permeability to water in the longitudinal direction (of the log) for three wood species, pine (Pinus sylvestris), birch (Betula pendula), and eucalyptus (Eucalyptus grandis). The wood species were cooked to a certain degree under kraft cooking conditions. The effect…

Kinetics of Aldehyde Oxidation by Chlorous Acid.

ABSTRACT Chlorous acid is known to react with aldehydes. This study investigated the oxidation kinetics of different aldehydes by chlorous acid. Reaction rates with chlorous acid at 25 °C were obtained for formaldehyde (11.0 M−1 s−1), vanillin (0.59 M−1 s−1), veratraldehyde (1.00 M−1 s−1), benzaldehyde (5.6 M−1 s−1), glucose (3.39 × 10−3 M−1 s−1), glycolaldehyde (39.0 M−1 s−1), and 5-formyl-2-furancarboxylic…

Reactions of aldehydes with chlorous acid and chlorite in chlorine dioxide bleaching.

ABSTRACT The role of chlorine (III) compounds, i.e. chlorous acid (HClO(2)) and chlorite (ClO(2)(-)), in chlorine dioxide bleaching were investigated by treating different pulps with Cl(III). It was discovered that in addition to its fully inorganic reactions, chlorous acid is consumed by organic structures present in the pulp. These structures were assumed to be aldehydes. The aldehydes might exist already…

Specific Permeability of Wood to Water. Part 2: Perpendicular Specific Permeability of Steamed, Impregnated, and Kraft-Cooked Wood.

ABSTRACT A method for measuring the perpendicular specific permeability of wood specimens to water is presented, which is a modification of the method presented in part 1 of this work. The specific permeability in the perpendicular direction of the log of three wood species, pine (Pinus sylvestris), birch (Betula pendula), and eucalyptus (Eucalyptus grandis), was measured from kraft-cooked wood of…

Lignin oxidation mechanisms under oxygen delignification conditions. Part 3. Reaction pathways and modeling

ABSTRACT A detailed kinetic model for the lignin oxidation chemistry is presented. It is based mainly on the mechanisms and kinetics presented in the literature. Parameters that could not be found in the literature were regressed against the experimental data obtained from oxidation experiments with softwood kraft lignin. In addition to the detailed model for the chemistry, acid-base equilibrium reactions…

The Kinetics and Stoichiometry of the Reaction between Hypochlorous Acid and Chlorous Acid in Mildly Acidic Solutions.

ABSTRACT The kinetics and stoichiometry of the reaction between hypochlorous acid and chlorous acid was studied under mildly acidic conditions (pH = 2.5−4.7). The experiments were conducted in dilute solutions (10−4−10−3 M) at T = 5−25 °C. External buffer compounds were not used. Chlorous acid, chlorine dioxide, and chlorate concentrations were monitored with titrimetric methods. Rate coefficients and activation energies…

Chlorate formation in chlorine dioxide delignification-an analysis via elementary kinetic modeling

ABSTRACT Elementary kinetic modeling was used to study the mechanism of chlorate formation in chlorine dioxide delignification. Reaction conditions reflecting typical industrial processes (T = 50°C, pH 1.5–4) were examined. Fe mediated Cl(III) decomposition and a reaction between hypochlorous acid and chlorous acid (or their equilibrium counterparts) were found to be the major reaction routes responsible for chlorate formation at…

Modelling of chemical pulp bleaching.

ABSTRACT A predictive pulp bleaching model utilizing physical phenomenon models and chemical reaction kinetics is introduced. Examples dealing with buffering properties of pulps, mass transfer limitations in fibre wall, and the kinetics of hexenuronic acid hydrolysis were used to elucidate the use of the model.

Reactions and Kinetics of Cl(III) Decomposition.

ABSTRACT Several pathways leading to the decomposition of chlorite and chlorous acid have been published. In this study, both experimental and computational approaches have been applied to clarify the authenticity of the different routes. The decomposition of chlorine (III), i.e. chlorous acid and chlorite, was monitored with iodometric titration at changing chloride concentrations, temperature, and existence of iron (III) at…

Other scientific articles

Automating the NMR analysis of base oils: Finding naphthene signals.

ABSTRACT Base oils, as many other oil products, are mainly analyzed with dedicated techniques designed to characterize the performance of these products in their intended use, along with suitable analysis techniques such as MS or GC to provide basic chemical information about the constituents. However, the physicochemical properties of base oils are direct result of the chemical structures of the…

Presentations

Capturing the Man Made Cellulosic Fibre`s great opportunity

Heikki Hassi`s presentation in Avancell Conference available here: Capturing the Man Made Cellulosic Fibre`s great opportunity Presentation Table of Contents: Market Opportunity Challenges to Man Made Cellulosic Fibres How to meet the challenges? Conclusions