Nathalie Marlin

Titration of free phenolic groups in pulps 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract The ClO2 titration method for in situ measurement of free phenolic groups in pulp has been improved to minimize interferences from other groups susceptible to react with ClO2. The method is based upon the reaction between free phenolic groups and chlorine dioxide at a temperature of 0°C, in the presence of dimethyl sulfoxide. Theoretically, one free phenolic group consumes two molecules of ClO2. The pH of the ClO2 treatment was advantageously fixed at 6.7 using a phosphate buffer, and a new protocol was proposed to avoid any possible interference of quinone groups (either present in pulp or formed during the procedure) on the residual ClO2 titration step. The results obtained on isolated lignin samples were compared to those measured by 31P NMR spectroscopy. The ClO2 method gave substantially higher values, for reasons which deserve further investigation.

Pulp delignification with oxygen and copper(II)-polyimine complexes

Abstract Ten Cu(II)-polyimine complexes were tested as potential catalysts in oxygen delignification of softwood kraft pulps. The ligands were chosen from the terpyridine and the phenanthroline families, including several neocuproines. One diamine-phenanthrene (daphen) was also investigated. The main purpose was to examine whether the presence of methyl or phenyl substituents would direct the oxidation toward lignin. As a catalyst for comparison, unsubstituted 1,10-phenanthroline was selected, which is known to activate both delignification and carbohydrate degradation during oxygen bleaching of kraft pulp. The variation of ligands was aiming at the complex solubility and redox potential of the parameters. The experiments were performed on a mixture of mechanical pulp and fully bleached kraft pulps, a fully bleached pulp alone, and an industrial unbleached pulp. Concerning the oxygen activation in delignification of kraft pulp, 4,7-diphenyl-1,10-phenanthroline was as good as 1,10-phenanthroline, but appeared to be more selective, which resulted in a higher DPv of cellulose after treatment. This was interpreted by the structural similarities between the ligand and the kraft lignin and by a better stability of the intermediate complex with lignin. Two Cu(II)-phenanthroline derivatives complexes (4,7- and 5,6-dimethyl-1,10-phenanthroline) were also identified as effective oxygen activators for the removal of native lignin.

Activated hydrogen peroxide decolorization of a model azo dye-colored pulp

Abstract Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H2O2) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H2O2 on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H2O2. A bleached kraft pulp was dyed with a model azo dye and submitted to activated H2O2 bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H2O2 color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH)2 would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH)2 as an activating species.

Study of the Direct Red 81 Dye/Copper(II)-Phenanthroline System

Recovered papers contain several chromophores, such as wood lignin and dyes. These have to be eliminated during paper recycling in order to produce white paper. Hydrogen peroxide under alkaline conditions is generally used to decolorize lignin, but its effect on dyes is limited. Copper(II)-phenanthroline (Cu-Phen) complexes can activate the oxidation of lignin by hydrogen peroxide. Hydrogen peroxide may also be activated during recycled fiber bleaching, thus enhancing its color-stripping efficiency towards unoxidizable azo dyes. The purpose of this paper was to determine the effect of Cu-Phen complexes on a model azo dye, Direct Red 81 (DR81), in aqueous solution. Different Cu-Phen solutions (with different initial Cu:Phen molar ratios) were prepared and mixed with the dye at different pHs. The geochemical computer program PHREEQC allowed precise calculation of the theoretical distribution between different possible coordinates (CuPhenOH+, Cu(Phen)22+, CuPhen(OH)2, Cu(Phen)32+, etc.) depending on pH and initial concentrations. UV-vis spectroscopic measurements were correlated with the major species theoretically present in each condition. The UV absorbance of the system was mainly attributed to the Cu-Phen complex and the visible absorbance was only due to the dye. Cu-Phen appeared to reduce the color intensity of the DR81 dye aqueous solution under specific conditions (more effective at pH 10.7 with Cu:Phen = 1:1), probably owing to the occurrence of a coordination phenomenon between DR81 and Cu-Phen. Hence, the ligand competition between phenanthroline and hydroxide ions would be disturbed by a third competitor, which is the dye molecule. Further investigation proved that the DR81 dye is able to form a complex with copper-phenanthroline, leading to partial color-stripping. This new “color-stripping effect” may be a new opportunity in paper and textile industries for wastewater treatment.

Modeling kraft cooking kinetics of fiber mixes from TMP and unbleached kraft pulps for assessment of old corrugated cardboard delignification

Abstract Kraft cooking kinetics of three different lignocellulosic substrates have been investigated, namely fibers from unbleached kraft pulp (UBKP from Pinus radiata), fibers from softwood unbleached thermomechanical pulp (TMP), and wood chips for TMP production. UBKP and TMP were considered to be representative of a fiber mixture obtained after the pulping and cleaning of old corrugated cardboards (OCC). The characteristic parameters for fitting a mathematical model for kraft pulping were estimated. Based on the results, a “fiber mixture cooking model” was developed to predict the cooking kinetics of TMP/UBKP mixes, accounting for the proportion of each component. The aim was to tailor OCC upcycling in terms of high quality products, which can be used for various purposes including paper and non-paper applications.

New insights into the decomposition mechanism of chlorine dioxide at alkaline pH

Abstract The mechanism of chlorine dioxide (ClO2) decomposition in an alkaline medium has been investigated. The formation of radicals and chlorinated species was studied in aqueous solutions containing ClO2 and simple model compounds of lignin or cellulose (vanillin, vanillyl alcohol, veratryl alcohol, methylglucoside and cellobiose) at acidic and alkaline pHs. Because hypochlorite (ClO−) is an intermediate occurring in the course of the reaction mechanism, similar experiments were carried out with solutions of sodium hypochlorite (NaClO) at alkaline and acidic pHs. Electron paramagnetic resonance (EPR) spectroscopy based on the spin-trapping technique revealed the presence of hydroxyl radicals (HO˙) at alkaline pH with ClO2 alone or with model compounds. At the same pH, only a small amount of HO˙ was detected with ClO−. Chlorite (ClO2−) and chlorate (ClO3−) ions were dosed with iodometric titrations, both during ClO2 alkaline decomposition and during reactions with model compounds. Vanillin and vanillyl alcohol were oxidized by ClO2. The intermediate ClO2− was either inert or reacted with the aldehyde function of vanillin. Cellobiose was attacked only in an alkaline medium, either directly by ClO2 or indirectly by HO˙ radicals. This resulted in the formation of glucose, which was then degraded by ClO2− ions. The generation of HO˙ could be one reason for cellulose degradation by ClO2 at alkaline pH, but possibly not the unique one, as it was not proved in this article, whether or not ClO2 is able to directly attach the OH functions of anhydrosugars at alkaline pH.

Innovative Ozone/Oxygen Reactive Flotation for Paper Deinking

To improve paper recycling, the potential of an innovative deinking process using a reactive ozone/oxygen gas mixture instead of air was studied on two recovered paper furnishes (offset print and newsprint/magazine mixture). Using suitable O3 concentrations, ink removal, following first-order kinetics, increased and losses dropped leading to better selectivity than using air alone. The ozone benefits in term of selectivity depended on temperature and paper furnishes and reached 100% for newsprint/magazine furnish at ambient temperature. Finally deinking effluent COD was significantly reduced and the ozone-based flotation allowed the reduction of the alkaline chemistry used before flotation.

WITHDRAWN: Elucidation of structural condensation in lignin of eastern cottonwood

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