Y. Ni

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...

UV-VIS SPECTRA OF LIGNIN MODEL COMPOUNDS IN THE PRESENCE OF METAL IONS AND CHELANTS

The presence of transition metal ions, such as iron, in lignin rich pulp fibers has negative consequences on pulp brightness and brightness stability. Earlier studies showed that impregnation of lignin-rich pulps with chelants, such as DTPA and EDTA, is very effective in recovering the brightness loss and reducing both the photo-yellowing and thermal yellowing of mechanical pulps. In this study, the fundamentals associated with such a process are further studied with lignin model compounds in combination with UV-Vis spectroscopicy. Four lignin model compounds, guaiacol, veratrole, vanillin and creosol, were tested. It was found that transition metal ions and lignin model compounds by themselves did not exhibit significant absorbance in the visible light range. However, when the two components were combined, a significant visible absorbance was observed. This was explained by the formation of coloured complexes between the transition metal ion and lignin model compounds, and transition metal ioniinduced coupling reactions. Among the transition metal ion species studied Fe(III), Fe(II), Cu(II), Mn(II) and Al(III),Fe(III) showed the strongest effect. In most cases, addition of a chelant to solutions containing transition metal ions and a lignin model compound reduced absorbance in the visible light range and blocked the coupling reactions. Furthermore, the EDTA-and DTPA-metal ion complexes exhibited ultraviolet shielding properties, which could be partly responsible for reduced photo-yellowing, when lignin-rich pulps are chelated.

Influence of Lignins on the Degradation of Cellulose During Ozone Treatment

Abstract Three lignin-carbohydrate model systems were studied to determine the mechanism of the effect of lignin on cellulose degradation during ozone bleaching. The three model systems are: methyl β-D-glucopyranoside, dextran and fully-bleached kraft pulps in the presence of various lignin model compounds. It was found that the lignin models can both promote and suppress the degradation of the carbohydrate during ozone treatment. The presence of the lignin models can exhibit a protective effect by competing with the carbohydrates for the ozone available in the system. On the other hand, the ozone-lignin reactions give rise to the formation of hydroxyl radicals which promote the carbohydrate degradation. It is suggested that much more hydroxyl radicals are formed via the ozone-lignin reaction route than via ozone self-decomposition. Among the lignin model compounds studied, the phenolic lignin structures have a more pronounced effect on carbohydrate degradation. This is explained by the easier formation o...

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.

Formation of Oxalate from the Mg(OH)2‐Based Peroxide Bleaching of Mechanical Pulps

Abstract Oxalate is a major source of scaling during the manufacturing process of bleached mechanical pulps and the majority is formed during the peroxide bleaching stage. In this paper, we investigated the effect of using Mg(OH)2 as an alkali source during peroxide bleaching on the formation of oxalate and its partition between soluble and precipitated oxalates. We found that at the same brightness target, the total amount of oxalate formed is similar between the Mg(OH)2‐based peroxide system and the conventional NaOH‐based system, however, almost all of the newly formed oxalate from the former was found in the soluble state, while in the NaOH‐based peroxide process, a large fraction is in the precipitate form. Therefore, the oxalate‐related scaling is significantly less or even negligible during the Mg(OH)2‐based peroxide process. The underlying mechanism accounting for the above observation will be discussed.

Using DTPA to decrease manganese-induced peroxide decomposition

Abstract The catalytic activity of Mn(+II) and Mn(+III) in decomposing hydrogen peroxide was studied by using DTPA as the only stabilizer. It was found that the addition of DTPA to a Mn(+II) containing system is more effective than if it is added to a Mn(+III) containing system. To decrease the catalytic effect of Mn(+III), sodium borohydride and DTPA under an acidic condition were considered to reduce Mn(+III) to Mn(+II). The effect of pH on using DTPA to decrease Mn-induced peroxide decomposition is discussed.

Interactions of Optical Brightening Agents With High Yield Pulps

Abstract The interactions of Optical Brightening Agents (OBA) with High Yield Pulp (HYP) fibers under two methods of OBA addition were evaluated on a softwood TMP and hardwood (aspen) HYP: OBA added to the peroxide bleach liquor (Method A), and OBA added conventionally at the wet end (Method B). The treated pulps were fractionated and OBA retention and efficiency in each fraction were determined. Adding OBA to the bleach liquor gave a higher OBA retention than adding OBA at the wet end; the hardwood HYP had a higher OBA brightening efficiency than the softwood TMP. The results are explained in terms of pulp morphology, lignin content, and process conditions (temperature and contact time). Adding OBA to the mechanical pulp also improved the brightness stability during the light-induced yellowing process.

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...

A Model Compound Study: The Formation of Colored Metallic Extractive Complexes and Their Effect on the Brightness of Tmp Pulp

Abstract Flavonoids, such as Quercetin, are the main polyphenol compounds found in extractives. When complexing with transition metal ions, these extractives may induce a significant discoloration to mechanical pulps. In this study, the effect of metallic extractive complexes was investigated using a model compound, Quercetin. It was confirmed that the complexes formed between some metal ions and Quercetin are strongly colored. However, most of the strong absorbance in visible light due to metallic Quercetin complexes, can be eliminated by the addition of diethylenetriaminepentaacetic acid (DTPA). The metal ions studied were Fe(III), Cu(II), Mn(II) and AI(III).

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...