Strategies to reduce the brightness reversion of industrial ECF bleached Eucalyptus globulus kraft pulp

BACKGROUND: Brightness stability is a key property of bleached chemical pulps and is primarily determined by wood species and bleaching process conditions. Eucalyptus globulus is becoming a very important raw material for hardwood pulp production. In spite of this importance, there is a relative lack of systematic studies in the literature dealing with the subject. This research aims to study the effect of some of the foremost bleaching parameters of a DEDD bleaching sequence as well as the effect of a final P stage (DEDP instead of DEDD) in the brightness stability of bleached E. globulus kraft pulps. RESULTS: The increase of the D₀ stage temperature from 55 °C to 90 °C caused an increase in brightness stability. Increasing the ClO₂ charges from 2.8% to 3.2% also improved significantly the brightness stability. A high H₂SO₄ charge in the D₀ stage (10 kg tonne^?1 pulp) diminished the brightness stability. The combination of H₂O₂ addition to the E stage and ClO₂ reduction in the two final D stages does not affect brightness reversion. Raising the D₂ stage temperature from 65 °C to 82 °C decreased the brightness reversion, while an increase was obtained when the temperature rose above 82 °C. Substitution of the last ClO₂ stage in the DEDD sequence by a H₂O₂ stage (DEDP) significantly reduced the brightness reversion. CONCLUSION: For an existing pulp mill in which the implementation of new technologies to improve brightness reversion is considered, the results obtained showed that brightness stability can be improved without any significant capital investment. Copyright © 2007 Society of Chemical Industry     

Mg(OH)2引入方式对纸浆过氧化氢漂白工艺的影响

引言制浆造纸工业是废水和污染物排放的重要源头之一。传统含氯漂白会产生多种难降解、对环境具有高危害的含氯有机化合物,因此它们正在被过氧化氢漂白等无氯漂白工艺所取代。纸浆中的过渡金属离子可催化过氧化氢无效分解并形成对纤维素破化性强的自由基,因此常采用漂前酸洗、螯合及漂白保护剂等来消除和抑制过渡金属离子的影响。而如何使保护剂的功效得到更好的发挥,是     

Behavior of Eucalyptus Kraft Pulp Extractives Components across ECF Bleaching and Their Impact on Brightness Reversion

Abstract

This study investigated the chemical composition of the dichloromethane and acetone extracts of eucalypt pulp across D(EP)DP and AZDP bleaching sequences by gas chromatography-mass spectrometry (GC-MS). The bleaching stages led to the partial removal and to several oxidative transformations of fatty acids and sterols, the main lipophilic extractives found in the unbleached pulp. The pulp samples were bleached to 90–91% ISO by D(EP)DP and AZDP sequences and their brightness stability and chemical characteristics determined. The effect of aging on brightness was investigated. The AZDP bleaching sequence resulted in pulps of higher brightness stability. Furoic structures representing the main acid degradation products of HexA are suggested as the actual intermediates that cause yellowing by forming colored compounds. The AZDP process removed larger amounts of HexA across bleaching.     

Kinetics of hydrogen peroxide bleaching of ALCELL® derived pulp

In this study, a kinetic model of the final bleaching stage with hydrogen peroxide in a totally chlorine free (TCF) bleaching sequence for ALCELL® processed pulp was developed. The model was based on the rate of chromophore destruction characterized by the decrease in the light absorption coefficient of bleached pulp at 457 nm, C_K. Based on the fact that the chromophore destruction proceeds rapidly in an initial phase followed by a much slower reaction during which a “floor-level” chromophore concentration is approached asymptotically, we propose that the hydrogen peroxide stage of the ALCELL® derived pulp in the studied TCF sequence consists of two distinct phases. The initial phase is a very fast reaction. The rate equation of the second phase was determined as: which is valid in a pH range of 10.5 to 11.5 and a temperature range of 60 to 92.5°C.     

烷基多苷的过氧乙酸漂色及组合漂色工艺研究

对烷基多苷(APG)的过氧乙酸(CH3COOOH)漂色工艺进行了优化,优化条件是:烷基多苷(APG)水溶液的浓度为50%,CH3COOOH用量为5%,漂色时间90 m in,漂色温度80℃,初始pH 12~12.5。在此条件下漂色,可使APG水溶液的消光系数由6~7降至0.4左右;采用质量分数分别为3%的H2O2与CH3COOOH组合漂色,可使漂色效果进一步提高;对H2O2与CH3COOOH漂色前后的APG样品进行了红外光谱对比分析。     

过氧化氢氧化再生纤维素及其阻燃、吸附性能

以过氧化氢氧化再生纤维素(GC)制备羧基再生纤维素(OGC),表征OGC结构变化及其对阻燃和吸附性能影响机理。通过碱泡预处理能有效提高GC比表面积,增加反应效率,获得羧基含量达15.6%的OGC。FT-IR和¹³C NMR表征结果说明OGC葡萄糖基环上的C₆位伯羟基能被选择性氧化成羧基。随着羧基含量的提高,OGC无定形部分溶解而提高其结晶度,晶型则无显著变化,OGC的热分解温度下降,但是成炭率显著提高。当添加6.25%OGC为成炭剂用于环氧树脂膨胀型阻燃时,氧指数达到27.2,阻燃等级为V0。以火焰原子吸收分光光度法测定结果表明,当羧基含量为15.6%,OGC对铅和铜离子吸附量分别提高14倍和3.5倍,其原因在于氧化改性能显著提高OGC的比表面积和容积率,增加吸附容量。研究结果说明以过氧化氢氧化制备的OGC在阻燃成炭剂以及金属离子吸附领域中具有良好的应用前景。     

Mechanism and kinetics of chlorine dioxide reaction with hydrogen peroxide under acidic conditions

The reaction of chlorine dioxide with hydrogen peroxide was studied in a well stirred batch reactor in a pH range of 3.60 to 5.07, which is of interest for commercial chlorine dioxide bleaching of chemical pulp. The reaction rate was determined by following the consumption of chlorine dioxide and hydrogen peroxide and the formation of chlorite. The rate equation was established. It was found that the concentration dependencies of chlorine dioxide, hydrogen peroxide and hydroxide ion were all first-order. A reaction mechanism compatible with the rate equation was proposed. Since it was found in previous work that chlorite in chlorine dioxide solution by the addition of small amount of hydrogen peroxide potentially led to a decrease in the formation of organically bound chlorine during chlorine dioxide bleaching, two methods were suggested to implement this technique in a bleach plant.     

In situ paired electrooxidative degradation of formaldehyde with electrogenerated hydrogen peroxide and hypochlorite ion

Formaldehyde was degraded with hydrogen peroxide and hypochlorite ion electrogenerated by paired electrolysis of dissolved oxygen and chloride ion in aqueous solution. Degradation of formaldehyde in the cathodic compartment was significantly affected by the ratio of electrolyte volume to cathodic surface area, oxygen sparging rate and stirring rate. The model calculations correlated sufficiently well with the experimental results. The average current efficiency and degradation fraction of the in situ paired electrooxidative degradation of formaldehyde were experimentally found to be 62.0% and 93.2%, respectively.     

Eucalyptus globulus kraft process modifications: Effect on pulping and bleaching performance and papermaking properties of bleached pulps

BACKGROUND: Increasing the yield of the wood pulping process allows the reduction of specific wood costs. Process modifications with a great impact on pulp yield are the profiling of chemical charges and addition of anthraquinone (AQ). The aim of the present work is to investigate the influence of effective alkali (EA) profiling and addition of anthraquinone on E. globulus kraft pulping performance. The impact of such process modifications on the ECF bleaching process and on the papermaking properties of the resulting bleached pulps is also evaluated. RESULTS: An EA profiling cook may lead to a pulp yield gain, which is more significant as the total EA charge used in the kraft cook increases. AQ addition to kraft pulping leads to a significant yield increase. The ClO₂ charge required to fully bleach the pulps is lower for EA profiling and higher for kraft + AQ unbleached pulps. Bleached AQ pulp presents a high beatability due to high pulp xylan retention. CONCLUSION: A low total EA charge is the key parameter for high polysaccharide retention on pulp. AQ addition constitutes a feasible strategy to increase pulp yield. Bleaching performance and papermaking properties of pulps produced with the three different methods may be affected by the kraft pulping modifications. Copyright © 2008 Society of Chemical Industry     

甲酸光催化降解过程中的过氧化氢生成机制

考察了在3种紫外光源（黑光灯、杀菌灯、臭氧灯）的照射下,分别以TiO₂ 与 Pd/TiO₂为催化剂,甲酸降解过程中过氧化氢的生成机制.研究发现,在黑光灯/催化剂条件下,可在纯水中生成过氧化氢,但当催化剂缺失时几乎不能生成.在黑光灯或杀菌灯照射下,甲酸溶液在有催化剂存在时可被稳定分解,但当催化剂不存在时则分解非常缓慢.对各种光源而言,Pd/TiO₂比TiO₂催化降解甲酸的效果好.对光源条件的比较发现,甲酸分解速度与过氧化氢生成速度依次为臭氧灯>杀菌灯>黑光灯.结果表明,甲酸光催化分解初速度与过氧化氢生成的初速度呈正比,过氧化氢生成是光催化降解有机物的关键因素.     

Aqueous degradation of atrazine and some of its main by-products with ozone/hydrogen peroxide

This laboratory study was designed to investigate the removal of atrazine (ATZ) and its first main by-products, deethylatrazine (DEA) and deisopropylatrazine (DIA) by O₃/H₂O₂. At least 76% of the oxidation rate of atrazine is due to free radical reactions. At neutral pH and 20°C, an initial hydrogen peroxide concentration of 10⁻³ M is optimum to reach a maximum oxidation rate of these compounds. Experimental results of oxidation in the presence of high hydrogen peroxide concentrations allow the mass transfer coefficient of ozonation to be determined. This coefficient, reactor flow analysis and kinetic data obtained have been applied to mol balance equations of atrazine, deisopropylatrazine, deethylatrazine, ozone (both in the gas and water) and hydrogen peroxide to obtain their corresponding concentrations at different conditions. © 1998 SCI     

反应介质对氢氧直接合成过氧化氢的影响研究

以超声浸渍法制备的PdO／γ-Al2O3-U为催化剂,考察不同无机酸、不同硫酸浓度对氢氧直接合成过氧化氢的影响。结果表明：酸性介质有利于氢氧直接合成过氧化氢,当反应介质为H2SO4溶液时,氢氧直接合成过氧化氢收率好于其他,其最佳浓度为0．35mol／L。     

The study of vapour phase hydrogen peroxide decontamination process as a potential method for degradation of organic pollutants

BACKGROUND: The work is focused on the application of vapour phase hydrogen peroxide (VPHP) as a highly promising and effective decontamination technique. The aim of this work was to assess the use of this validated technique for the removal of chemicals from contaminated surfaces and examine the impact of key parameters on the course of the decontamination process. RESULTS: Unique sophisticated laboratory equipment was developed to test the effect of VPHP on chemical substances. It was used for the evaluation of the role of crucial parameters such as the relative humidity, condensation and synergistic effect of UV radiation on the VPHP agent efficiency on a model compound (vanillin) degradation. The degradation rate of the model substance was notably affected by all these factors. CONCLUSION: VPHP could be used for an efficient decomposition of vanillin. The course of the decontamination process was strongly influenced by condensation (showing a substantial difference between ‘wet’ and ‘dry’ processes) and the synergistic effect of UV radiation influencing the reaction rate and degree of decomposition. Copyright © 2010 Society of Chemical Industry     

蒽醌法生产过氧化氢中降解物的生成和再生

综述了以2－乙基蒽醌（EAQ）和四氢－2－乙基蒽醌（H4EAQ）为工作载体的蒽醌法生产过氧化氢过程中生成的各种降解物的化学组成和分子结构的分析确定。介绍了一些降解反应机理，提出将工作液中有效蒽醌的降解分为氢化降解和氧化降解两种，氢化降解又可分为有效蒽醌中芳环的氢化和羰基的氢解。使用碱性氧化铝、酸、碱、过氧化物和有机胺等再生剂再生工业生产中长期使用工作液中的降解物，取得了良好的再生效果，再生后工作液中的有效蒽醌均有明显增加。     

Three-month evaluation of a low concentration (6% hydrogen peroxide) experimental bleaching gel containing Tio2 and chitosan: An in vitro study

The study aimed to compare the effectiveness of an experimental gel that contained 6% hydrogen peroxide, titanium dioxide (TiO₂), and chitosan nanoparticles with that of the two bleaching agents that are routinely used and evaluate their effectiveness in a 3-month period. Seventy-two extracted premolar teeth were divided into three groups for the bleaching procedure. TiO₂ and chitosan were added to increase the whitening effect of the low-concentration experimental gel. In group 1, the experimental gel was applied and activated with a D-Light Duo LED device. In group 2, Opalescence Boost PF was applied chemically. In group 3, Philips Zoom was applied and activated with Zoom Advanced Power. The color of the teeth was measured with a Vita Easyshade Advance 4.0 spectrophotometer before the bleaching and 24 hours, 7 days, 14 days, 30 days, and 3 months after final bleaching. The CIEDE2000 color differences (∆E₀₀) and average L*, a*, and b* values were calculated. Effective bleaching was observed in three groups as determined by the initial color at different measurement times (P < .05). Philips Zoom showed a higher value of color change than the other groups at all times. The experimental gel showed a bleaching activity like that of Opalescence Boost PF at all-time measurements. A slight decrease in color change was observed between the first-month measurement and third-month measurement in all groups. A low-concentration experimental gel containing TiO₂ and chitosan provided effective whitening, and the whitened color persisted throughout the 3-month period.     

钯催化剂双氧水装置生产初期控制要点分析

以台湾南亚公司双氧水装置为例，介绍了钯催化剂固定床生产初期所遇到的一些常见问题及控制手段。即，在开车初期应通过使用氮气来控制氢化塔的压力，氢气的安全量可控制为工作液流量的5倍，氢化塔温度波动范围控制不超过1℃，加强对工作液组分的控制，保证系统的稳定性。     

Oxidation of hydrocarbons by hydrogen peroxide over Ti catalysts: Kinetics and mechanistic studies

n-hexane conversion to hexanols and hexanones as well as the conversion of 2- and 3-hexanol to 2- and 3- hexanone, by reaction with aqueous hydrogen peroxide on titanium silicalite were the objects of kinetic investigations. The choice of these reactions is justified on the basis of an analysis of literature dealing with partial oxidation reactions performed on Ti sites in silica environments. The kinetic analysis based on equations derived using the mathematical theory of linear graphs allows several conclusions on the nature of surface intermediates and on the reaction mechanism. These conclusions are discussed in terms of the partial oxidation of organic materials by hydrogen peroxide over Ti catalysts. This review paper relies mostly on work by the authors and it intends to make an integrated presentation of the kinetics of some critically significant catalytic oxidation reactions. The content was the subject of a plenary lecture at the 5^th symposium of the Romanian Catalysis Society.     

过氧化氢生产技术和市场现状及展望

介绍了中国过氧化氢技术发展的沿革以及现有生产能力和技术水平，对国内外过氧化氢技术现状进行了对比。详细阐述了过氧化氢生产中几个关键工序（氢化、氧化、萃取和后处理）的作用及易出现的问题。同时也对过氧化氢产品的市场发展特点及趋势作了描述，提出了中国今后过氧化氢技术发展的希望。