Efficient total halogen-free photochemical bleaching of kraft pulps using alkaline hydrogen peroxide

Total halogen-free bleaching of kraft pulps was conducted by an oxidative photochemical process at room temperature using alkaline hydrogen peroxide. Selection of an appropriate wavelength of light was crucial for effective bleaching and avoiding degradation of cellulose. The wavelength of the light has to be selected so that the light is absorbed only by the colored compounds in the pulps and not by the bleaching reagents or the pulp itself. When a long-wavelength black-light fluorescent lamp was used in combination with aqueous hydrogen peroxide solution at pH 11, the bleaching efficiency for hardwood and softwood kraft pulps reached the same level as that obtained by conventional two-stage elemental chlorine-free processes.     

Analysis of pitch deposits produced in kraft pulp mills using a totally chlorine free bleaching sequence

Two organic deposits accumulated in a Kraft pulp mill during pulping of Eucalyptus globulus wood and throughout a TCF (totally chlorine free) bleaching sequence were characterized. One deposit was collected after cooking and an oxygen delignification stage while the other was collected after bleaching with hydrogen peroxide. The deposits were Soxhlet extracted with acetone, and the extracts redissolved in chloroform and subsequently analyzed by gas chromatography (GC) and GC-mass spectrometry (MS) using short and medium length high temperature capillary columns, respectively. On the other hand, the insoluble residues left after the acetone extraction were analyzed by Curie-point flash pyrolysis-GC-MS and by pyrolysis-methylation-GC-MS. The compounds identified in the deposits arise from the E. globulus wood lipophilic extractives that survive the pulping and bleaching processes. Triglycerides were completely hydrolyzed during the Kraft cooking and the fatty acids dissolved. Steroids (alcohols, hydrocarbons, ketones and esters) and waxes were the main components in the deposit collected after the oxygen delignification stage. After the bleaching with hydrogen peroxide, content of the waxes were reduced and fatty acids appeared. High amounts of fatty acids salts were also identified in the deposit collected after the oxygen stage, and in minor amounts in the deposit collected after hydrogen peroxide bleaching. In contrast, this deposit was mainly made up of high amounts of lignin-derived phenolic moieties.     

Reactions of chlorine dioxide with organic compounds. Selective oxidation of sulfides to sulfoxides by chlorine dioxide

A novel method for the selective oxidation of various types of sulfides to sulfoxides using chlorine dioxide as the oxidant is proposed.     

The colloidal behaviour of kraft lignin

Kraft lignin gels have been found to exhibit both macrosyneresis and hysteresis in swelling. The effects of temperature and prehistory on swelling and on the mechanical properties have been investigated. Thermal treatment of kraft lignin gels in the protonised state induces an irreversible deswelling of the gels. This irreversible deswelling can, however, be released by deprotonization of the carboxyl groups. Deswelling also occurs when partly dried protonised gels are placed in water again. Furthermore, the gels were found to exhibit pH-hysteresis.It is concluded that the above-mentioned effects are closely related to the state of dissociation of the carboxylic groups and to their ability to form intermolecular hydrogen bonds in the network structure.It is suggested that syneresis is due to a structural rearrangement induced by breaking and formation of hydrogen bonds and promoted by the long-range van der Waal's interaction between the colloidal units in the gel. Swelling hysteresis is assumed to be related to repeptization phenomena commonly encountered in lyophobic colloids.     

Reactions of terpene alcohols and diols with chlorine dioxide in dimethylformamide

The system chlorine dioxide–dimethylformamide in combination with or without a catalytic amount of MoCl₅, CeCl₃, ZrOCl₂, or VO(acac)₂ induces oxidative chlorination of a number of bicyclic terpene alcohols and vicinal diols. 2α-Chloropinan-3-one, 3α-chloro-10β-pinan-4-one, 5α-chloro-3α-hydroxycaran-4-one, 5β-chloro-3β-hydroxycaran-4-one, and 4α-chloro-2α-hydroxypinan-3-one were thus synthesized in good preparative yields.     

The colloidal behaviour of kraft lignin III. Swelling behaviour and mechanical properties of kraft lignin gels

Summary Kraft lignin gels have been synthesized by cross-linking kraft lignin (Indulin ATR) in water with varying amounts of epichlorohydrin under alkaline conditions. The effects of pH and salt concentration on the swelling behaviour and on the mechanical properties of these gels have been investigated.Swelling was determined gravimetrically and the mechanical properties of the gels were tested under uni-axial compressive creep in the time interval 1–900 s. The gels show a linear viscoelastic behaviour without viscous flow.The kraft lignin gels exhibit a swelling behaviour typical for polyelectrolytic networks, i. e. the degree of swelling increases with an increasing number of ionized groups and decreases with increasing salt concentration. The swelling behaviour and ion exchange capacity were found to be nonspecific towards type of alkaline solution (LiOH, NaOH, and KOH).The ability of the carboxylic groups to form intermolecular hydrogen bonds has a strong influence on the mechanical properties of the gels. Creep compliance and creep rate increase greatly when the carboxyl groups are dissociated. It is therefore concluded that the effective number of crosslinks in the networks in addition to chemical cross-linking is also dependent on the state of dissociation of the carboxylic groups.With 11 figures and 1 table     

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.     

Determination of fiber charge components of Lo-solids unbleached kraft pulps

Four different titration methods for measurement of fiber charge were used in this study. Each method gave different fiber charge values depending on the acidity of the end point and the interaction between the fiber chemical components and the titrant. Also, the interactions between the ionizable groups on the fiber had significant effects on the interpretation of these results. The conductometric titrations showed trends similar to the results obtained from the potentiometric titration. The conductometric titrations with NaOH produced higher fiber charge values, higher than the titrations with NaHCO(3). The differences between the results obtained from the potentiometric and polyelectrolyte titrations, which were associated with the dissolved fiber components during the delignification, were linearly related to the Kappa number of pulps. The positive intercept of this linear relationship indicated that the kraft pulping process not only removed the ionizable groups associated with the dissolved components, but at the same time provided conditions to form new ionizable groups in the fibers. The polyelectrolyte titration results indicated that the lignin content in the fibers did not affect the fiber surface charge. Data extracted from the FTIR spectra of protonated fibers were highly correlated with the fiber charge values obtained from the conductometric titration with NaOH.     

Surface characterization of unbleached kraft pulps by means of ESCA

The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by electron spectroscopy for chemical analysis (ESCA). The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Examination of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer and that it decreases linearly with decreasing kappa number. The concentration of alkyl carbon is decreased by extraction of the fibres with dichloromethane, but the amount remaining in the surface after extraction still decreases linearly with decreasing kappa number (i.e. it decreases with increasing digestion time). It is suggested that the observed enrichment of alkyl carbon in the outermost surface layers most probably is due to reprecipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of digestion time. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.     

Reactions of chlorine dioxide with organic compounds. 2. Oxidation of thiols

The method for the synthesis of 4-aryl-2,6,6-trimethyl-5-oxo-5,6-dihydro-4H-thieno[3,2-b]pyrroles from accessible 4-aminothiophene derivatives was developed.     

Reactions of chlorine dioxide in dichloromethane I. Formation of radical cations in acid media

Chlorine dioxide oxidises electron rich organic compounds to the corresponding radical cations in dichloromethane/TFA medium. In a different experimental set up using alkaline biphasic solvent system, its utility as hydrogen abstractor has been capitalized in the preparation of diazodiphenyl methane in good yield.     

The role of stilbenes in bleaching and colour stability of mechanical pulps. I. The reaction of lignin model stilbenes with alkali and oxygen

The reactions of lignin model hydroxystilbenes and TMP with alkaline hydrogen peroxide and with alkali and oxygen have been studied to determine the susceptibility of stilbenes, to oxidative degradation. Oxygen in the presence of alkali readily destroys lignin model stilbenes via cleavage of the olefinic double bond. The stilbene must contain a ring hydroxyl substituent for the reaction to occur. The reaction is fastest if the stilbenes havep,p′-dihydroxyl substituents. Stilbenes of the type likely to be attached to the lignin in pulps have only one hydroxyl group and are more stable. Hydrogen peroxide, by itself, is unreactive with stilbenes but the presence of oxygen as a peroxide decomposition product should limit the accumulation of stilbenes during alkaline peroxide bleaching of mechanical pulps. Alkaline peroxide bleaching of mechanical pulps under a pressurised atmosphere of oxygen gas leads to a slight increase in brightness and brightness stability. Guaiacyl-substituted stilbenes are more stable to alkali and oxygen than are syringyl-substituted stilbenes. This may partially explain why it is easier to bleach hardwood than softwood mechanical pulps.     

Rapid analysis of unsaturated acidic xylooligosaccharides from kraft pulps using capillary zone electrophoresis

Several acidic xylooligosaccharides containing unsaturated “hexenuronic acid” units, i.e. 4-deoxy-L -threo-hex-4-enopyranosy-lurinic acid (4-ΔU) units, were separated as their alditol derivatives by capillary zone electrophoriesis in 438 mM borate buffer (pH 10.3) and were detected selectively at the μM level on-column UV detection at 232 nm. These acidic oligosaccharides were obtained from birch and pine kraft pulps on enzymatic hydrolysis with endoxylanases and subsequent treatment with other Trichoderma reesei enzymes. Under the conditions empolyed, acidic 4-ΔU-containing xylooligosaccharides with a molecular size renging from trisaccharides up to nonasaccharides could be separated. Oligosaccharides with higher molecular mass were detected first. Two 4-ΔU-xylotetraose isomers, with the 4-ΔU-group linked to different xylose units in the iligosaccharide backbone, could be resolved from each other with a resolution of about 1. By using a disaccharide (4-ΔU α-(1 → 4) linked to N-acetyl glucosamine) as a model compound the minimum detectable concentration was determined as 10 μM.     

Influence of ozonized kraft lignin on the crystallization of CaCO3

Results are reviewed from a study examining how structural modifications introduced by ozonization enhance the influence of kraft lignin on the crystallization of CaCO(3). Ozone treatment of kraft lignin in an aqueous environment is shown to increase its carboxylic acid and overall oxygen content and reduce its molecular weight. Calcium concentration and temperature were monitored in heated supersaturated solutions containing ozonized kraft lignins to gauge their influence on CaCO(3) crystallization processes. The presence of kraft lignin raises the temperature necessary to induce crystallization. This effect is shown to level off at relatively low lignin concentrations and be dependent on the extent of ozone treatment the kraft lignin has undergone. A linear correlation is found between crystallization temperatures and the carboxylic acid content of ozonized lignin samples indicating the introduction of these functional groups plays an important role in enhancing its inhibitory effect. Scanning electron microscopy images of crystals grown in the presence of kraft lignins show significant morphological modifications. These are consistent with specific or pseudo specific interactions between the lignin and crystal faces of calcite to inhibit growth parallel to its c axis. The influence over crystal morphology demonstrated by modified kraft lignin increases with increasing ozonization. Also presented here are crystallization temperature data for a range of kraft lignin ultrafiltration fractions, which indicate that the optimal (nominal) molecular weight of kraft lignin for inhibiting the crystallization of CaCO(3) lies between 5000 and 10000.     

Reactions of cobalt oxide with chlorine

We report the thermodynamic calculations and experimental studies of the kinetics of the reaction of Co₃O₄ with chlorine at 300–850°C. The show that cobalt chloride sublimation is controlled by the rate of chloride evolution from the surface. The chlorination specifics of the oxides of iron-family metals are compared.     

High resolution spectrophotometry for identification of chlorine dioxide in concentrated chlorine solutions

Electrolyzed salt brine generators hold great promise for water disinfection in small communities and remote locations. Electrolysis cell liquors have been reported to contain chlorine, chlorine dioxide and ozone. High resolution spectrophotometry was used to observe the presence (or absence) of a unique spectral absorbance pattern present in solutions containing 1-2 mg/l chlorine dioxide.     

Reaction of chlorine dioxide with phenol

The kinetics of phenol oxidation with chlorine dioxide in different solvents (2-methylpropan-1-ol, ethanol, 1,4-dioxane, acetone, acetonitrile, ethyl acetate, dichloromethane, heptane, tetrachloromethane, water) was studied by spectrophotometry. In all solvents indicated, the reaction rate is described by an equation of the second order w = k[PhOH]·[ClO₂]. The rate constants were measured (at 10—60 °C), and the activation parameters of oxidation were determined. The reaction rate constant depends on the solvent nature. The oxidation products are a mixture of p-benzoquinone, 2-chloro-p-benzoquinone, and diphenoquinone.     

Oxidation of valeraldehyde by chlorine dioxide

The product of the reaction of valeraldehyde with chlorine dioxide was determined, and the solvent effect on the reaction kinetics was studied. The major oxidation product is valeric acid. The reaction rate is described by the second-order equation w = k[RCHO]·[ClO₂]. The rate constants were measured in the 297–328 K interval, and the activation parameters of the reaction were determined.