A. R. P. van Heiningen

Studies on the Reactions of Phenolic and Non-Phenolic Lignin Model Compounds with Chlorine Dioxide

Abstract The reaction between chlorine dioxide and four different lignin model compounds (phenolic and non-phenolic, with or without an α-hydroxyl group) are studied. The key difference with previous studies is the effective elimination of hypochlorous acid by sulfamic acid during chlorine dioxide treatment. The elimination of hypochlorous acid, an important intermediate formed during chlorine dioxide bleaching, makes it possible to study the consumption of the lignin model compounds solely as a result of the action of chlorine dioxide. Based on almost closed mass balances for the substrate and atomic chlorine it is found that the reaction between ClO2 and lignin model compounds is generally characterized by three independent parallel reactions: 1) demethylation, 2) formation of 2-methoxy-p-quinone and 3) formation of muconic acid monomethyl ester and/or its derivatives. Although, the importance of each reaction depends on the functional groups of the substrate, the demethylation reaction is the most impo...

MFO INDUCTION IN FISH BY FILTRATES FROM CHLORINE DIOXIDE BLEACHING OF WOOD PULP

Spent bleaching liquors from pulp bleached with chlorine dioxide were assessed for their potency to induce hepatic mixed function oxygenase enzymes (MFO) in rainbow trout, as indicated by activity of ethoxyresorufin-o-deethyase (EROD). Filtrates were collected from two kraft mills in Central Canada to assess the potency of filtrates from hardwood and softwood bleaching. All mill-scale bleaching filtrates induced MFO activity, and filtrates from softwood pulp bleaching appeared more potent than filtrates from hardwood bleaching. Filtrates from the final bleaching stage were most potent, and filtrates from the first stage were the least potent. In laboratory bench-scale bleaching experiments, pulp from softwood and hardwood kraft mills in Eastern Canada was bleached via an industry-standard 5-stage chlorine dioxide bleaching sequence. The filtrates were collected and used in fish bioassays to assess EROD-inducing potency. Potency of bench-scale filtrates varied depending on wood furnish (i.e. softwood vs. hardwood) and the bleaching stage, with all bench-scale filtrates being much weaker EROD inducers than mill-scale filtrates. Recycled paper mill washwater is a possible source of compounds causing increased potency of the mill-scale filtrates.

A Novel Ozone Bleaching Technology for the Alcell® Process

The ALCELL ® process is an ethanol-based autocatalyzed solvent pulping technology which is being developed by Repap Enterprises Inc. The paper will present a novel ozone bleaching process (Zn), which is compatible with the present ALCELL ® technology. It is based on that an acidified ethanol-water mixture is used as the pulp impregnation liquor during ozone bleaching. It was found that the presence of ethanol dramatically reduces that carbohydrate degradation while delignification is not affected. Process parameters in the Zn stage, including the ethanol concentration and pH, on the delignification efficiency and carbohydrate degradation were studied. The underlying mechanism of this novel bleaching technology will also be discussed.

The formation of gaseous products and its relation to pulp bleaching during the peracetic acid treatment

Abstract When used in pulp bleaching, peracetic acid is consumed by two competitive pathways: oxidation of pulp and wasteful reactions such as decomposition. In this paper, the peracetic acid consumed in wasteful reactions is quantified by determining the gaseous products evolved. It is found that although carbon dioxide is formed under certain conditions, oxygen is the dominant product of the wasteful reactions. The oxygen formation is directly proportional to the consumption of oxidants (as peracetic acid and hydrogen peroxide) in the wasteful reactions with 2 moles of oxidant consumed per mole of oxygen formed. Therefore, the brightening efficiency during peracetic acid treatment can be characterized by correcting the measured peracetic acid consumption for decomposition. The peracetic acid brightening results for an oxygen delignified softwood kraft pulp are reported. It is found that a significant amount of peracetic acid is consumed by the wasteful reactions during the brightening. The effect of pro...

Initial Delignification and Cellulose Degradation of Conventional and Ethanol-Assisted Ozonation

Abstract It has been proposed that the initial regime of pulp ozonation is a diffusion controlled process, due to the low solubility of ozone and its very fast reaction with lignin. However, whether the process is governed by diffusion on a fibre wall scale (macro diffusion control), on a (micro)fibril scale (micro diffusion control), or by reaction with lignin located on the fibre surface followed by diffusion control is an open question. In order to address this, a 31 kappa Hemlock kraft pulp impregnated with acidified (pH = 2.0) water or acidified (pH = 2.0) ethanol-water (70% w/w) was ozonated at high consistency in a differentially operated packed bed reactor. The cellulose degradation and pulp delignification rates were determined from the change in pulp viscosity and kappa number with ozonation time. Transmission electron microscopy (TEM) was used to visualize the lignin distribution of KMnO4 stained fibre walls. The TEM pictures clearly show reacted lighter regions at exposed fibre surfaces, which...

Development of Phenolic Lignin During ClO2 Bleaching of Kraft Pulp

Abstract The development of the phenolic lignin content in kraft pulp during ClO2 bleaching was quantitatively determined by the periodate oxidation method. The effect of hypochlorous acid, an intermediate formed during chlorine dioxide bleaching, was eliminated by addition of sulfamic acid, a scavenger of hypochlorous acid. It was found that the number of free phenolic lignin groups per 100 lignin monomer units decreased from about 29 for unbleached kraft lignin to about 6.5 after 1 minute of ClO2 bleaching. It was also shown that the in-situ generated hypochlorous acid created phenolic hydroxyl groups during chlorine dioxide bleaching. Since it was found that delignification by chlorine dioxide itself was mostly restricted to free phenolic lignin, these findings were used to explain the effect on delignification of addition order of chlorine and chlorine dioxide during bleaching of kraft pulp.

Characterisation of pulp demethylation during chlorine dioxide bleaching

SummaryThe methoxyl loss from softwood kraft pulp during chlorine dioxide treatment can be accounted for by methanol and the methoxyl content of dissolved organic material in the bleach filtrate. This was established by a methoxyl group mass balance made at different bleaching times. It was found that ClO2 rather than the in-situ generated hypochlorous acid is mainly responsible for the methanol formation. It was shown that fully methylated pulp is hardly demethylated by ClO2 under industrial ClO2 bleaching conditions when hypochlorous acid is effectively captured. Furthermore, the rates of formation of methanol and methoxyl group containing dissolved organic material are proportional to each other. The experimental evidence suggest that demethylation and delignification are closely related during ClO2 treatment of softwood kraft pulp.

A kinetic model for peracetic acid brightening of an ozone delignified softwood kraft pulp

A kinetic model of peracetic acid brightening of a solvent-assisted ozone delignified pulp was developed. The model consists of three parallel and one consecutive reaction, and is based on reaction pathways reported for lignin model compounds with peracetic acid. An optimization search algorithm was used to find the kinetic parameters of the model. The kinetic model provides an adequate description of the disappearance rate of the chromophores in pulp at constant pH and peracetic acid concentration.

The rate process of H2S emission during steam gasification of black liquor char

Abstract The chemical recovery cycle, a key component of a kraft pulp mill, produces energy and regenerates the active pulping chemicals, NaOH and Na 2 S, from the spent pulping liquor (called black liquor). The development of gasification-based recovery technology requires information on the rates of several interrelated chemical reactions, most importantly the gasification of carbon and sulfur in the char. The sulfur emission rate during steam gasification of black liquor char was studied as a function of temperature (600–700°C) and H 2 O and H 2 concentrations. The major sulfur-containing gas generated is H 2 S. Analyses of the experimental results obtained with a thermobalance system indicate that the H 2 S concentration in a 0.5 mm high char bed is at thermodynamic equilibrium. Therefore, the rate of H 2 S production is influenced by thermodynamics, the carbon gasification rate, gasification product distribution, and the mass transfer coefficient between the char bed and the surrounding gas phase. Based on thermodynamics, gasification kinetics, and a material balance, a simple expression for the H 2 S emission rate is derived. Good agreement is obtained between the measured and predicted rates.

Probing red maple pit membrane pore size at fiber saturation point and oven dry using polystyrene macromolecules

SummaryA modified solute exclusion technique was used to pressure impregnate a polystyrene molecular weight (MW) series dissolved in styrene into red maple samples at approximately the fiber saturation point (FSP) and oven dry (OD). Radial penetration was less than tangential and FSP less than OD. There was a marked change in radial OD penetration at 900,000 MW. There was no marked penetration change with MW in the tangential direction, although there appeared to be a slight decrease in FSP penetration at the higher MW tested.