A new electrochemical technique for bleaching cellulose pulp

A study of electrochemical bleaching of cellulose pulp was carried out in an electrolyte cell composed of a horizontal graphite anode and a parallel stainless screen steel cathode, using NaCl as electrolyte. Variables studied were: current density, sodium chloride concentration, pulp concentration, pH and temperature. The rate of bleaching was found to increase with increasing current density, salt concentration and temperature. The rate of bleaching was found to decrease with increasing pH and pulp concentration. Energy consumption ranged from 0.1 kWh kg^?1 (pulp) to 1.75 kWh kg^?1 (pulp), depending on current density and degree of bleaching. The quality of electrochemically bleached pulp was found to compare favourably with that of chemically bleached pulp.     

Bleach activation of thermomechanical pulp

Under mild alkaline condition the bleaching activator tetraacetyl ethylenediamine (TAED) forms peroxyacetic acid with sodium perborate and improves the brightness of thermomechanical pulp. The activator makes it possible to bleach the pulp efficiently even without addition of sodium hydroxide at any temperature in the range 40 to 70°C. A mathematical model has been proposed to allow estimation of the total peroxy acid consumption during activated bleaching process. Using this model it is possible to calculate the extent of peroxy acid decomposition by predetermining the rate constant and activation energy. The effect of bleach activation was found to be maximum at temperatures below 60°C. The influences of bleaching time, pH, consistency, temperature and TAED charge on the bleach activation has been evaluated. The activator is effective enough to improve the brightness of sodium perborate bleached pulp at an average charge of about 50 mass% of sodium perborate. Apparently, high consistency dispersive bleaching without free alkali is a technological and economic advantage of the process.     

Electrochemical treatment of pentachlorophenol in water and pulp bleaching effluent

Adsorbable organic halides (AOX) compounds produced during bleaching of pulp are recalcitrant and known to have eco-toxic effect. We have studied the removal of pentachlorophenol (PCP) as a model AOX compound in water as well as in pulp bleaching effluent of a bamboo based mill by electrochemical treatment in batch mode. It was found that 10 mg L⁻¹ of PCP in water was removed almost completely in <10 min at a current density of 6 mA cm⁻² in the presence of 1000 mg L⁻¹ NaCl serving as an electrolyte and source of chloride ions. The initial rate of PCP removal was found to decrease at alkaline pH (9.3) as compared to that at acidic pH (5.5). PCP removal in neutralized raw pulp bleach effluent (containing 1830 mg L⁻¹ of chloride) was very slow and incomplete even after 2 h of electrochemical treatment at a current density of 15 mA cm⁻². Various pretreatments of raw bleach effluent such as, alkaline sulfide using sodium sulfide, alkaline reduction using ferrous sulfate and coagulation using potash alum were evaluated. Electrochemical treatment of potash alum pretreated effluent (spiked with PCP) could achieve >90% removal of initial colour, COD and PCP in <1 h. The treatment scheme presented here may be a promising technology for removal of AOX, COD and colour from pulp bleaching effluent. The estimated cost of combined treatment (potash alum coagulation + electrochemical) is US$ 0.7–0.9 per cubic meter of the raw pulp bleach effluent.     

漆树漆酶催化甘蔗渣纸浆漂白的研究

利用漆树漆酶在无介体存在条件下对甘蔗渣纸浆进行生物漂白,初步探索了反应时间、漆树漆酶用量、温度及酸度对甘蔗渣纸浆白度的影响。结果表明,在浆浓为3%,漆树漆酶用量1.6 mL/g(对干浆),漂白时间20 min,反应温度20~50℃,pH值为6.1~8.1时,甘蔗渣纸浆白度可提高4%~5%ISO。     

Determination of Main Parameters Affecting Ozone Bleaching of Wheat Straw Pulp Using Plackett–Burman Design

Laboratory-scale studies were carried out on ozone bleaching of wheat straw soda pulp. Effects of five variables—pH, consistency, time, temperature, and ozone dose—on three pulp parameters— kappa number, brightness, and viscosity–were determined using Plackett–Burman experimental design. Results showed that for the parameter kappa number of pulp, ozone dose is the most important factor followed by pH and consistency. Pulp parameter viscosity is affected by factor pH, followed by consistency and ozone dose. Brightness of the wheat straw pulp mostly depends on factor ozone dose, followed by pH.     

A simplistic mechanistic model and effect of consistency on alkaline peroxide brightening of mechanical pulps

The multiple active site mechanistic model proposed earlier (Liu, Chem. Eng. Sci. 58 (2003) 2229) has been revisited and a simplistic “single active site” model has been developed. The effect of pulp consistency during brightening reaction has been examined based on the derived kinetic model. There are three competing factors affecting the brightening reaction arising from pulp consistency: effective chemical concentration in the brightening liquor, accessibility of chromophores to the active chemical agents, and frequency of the chromophore-chromophore contact. With the same brightening agent charges (on a dry pulp basis), increasing pulp consistency resulted in an increase in the effective brightening agent concentration in the brightening liquor and the brightening reaction rate increases as well as the final attainable brightness. Increase in pulp consistency under constant brightening agent concentration in liquor reduces brightening reaction rate and final attainable brightness due to the reduction of the accessibility of the brightening agents to the chromophore sites. Finally, increasing pulp consistency increases the frequency of chromophore contacts among different fibers and thus increases brightening reaction rate. Theoretical models are proposed for these effects and good agreement is found with existing experimental data.     

废报纸脱墨浆两段漂白工艺研究

研究了废报纸脱墨浆过氧化氢―过氧化氢(PP)、过氧化氢―甲脒亚磺酸(PF)两段漂白工艺。结果表明,废报纸脱墨浆PP漂白中第二段过氧化氢漂白的适宜工艺条件为:浆浓20%,漂白时间2.5 h,温度60℃,乙二胺四乙酸(EDTA)用量0.2%,硫酸镁用量0.05%,硅酸钠用量0.5%,过氧化氢用量4%,氢氧化钠用量0.5%,漂后浆白度71.5%(ISO);PF漂白中第二段甲脒亚磺酸漂白的适宜工艺条件为:漂白温度60℃,漂白时间40 min,浆浓10%,甲脒亚磺酸(FAS)用量1.6%,NaOH用量0.8%,漂后浆白度68%(ISO)。     

废报纸脱墨浆甲脒亚磺酸单段漂白工艺研究

主要研究废报纸脱墨浆甲脒亚磺酸(FAS)单段漂白工艺及影响因素,探讨了FAS用量、NaOH用量、温度、时间对纸浆白度的影响。结果表明,废报纸脱墨浆FAS单段漂白的适宜工艺条件为:FAS用量1.4%(对绝干浆),NaOH用量0.7%(对绝干浆),浆浓10%,漂白温度70℃,时间40 min,在此条件下漂后浆白度可达到59%(ISO)。     

Optimization of ozone bleaching conditions for improving wheat straw pulp quality using response surface methodology

Ozone bleaching conditions for wheat straw soda pulp were optimized using response surface methodology with central composite design. Effect of pH, consistency, and ozone dose on kappa number, brightness, and viscosity was investigated. Optimized process conditions to get minimum kappa number, maximum viscosity, and brightness were obtained as follows: pH 2.08–2.25, pulp consistency 27.4–30.0%, and ozone dose 0.4%. Validation of the model predicted values and experimental values obtained for optimum conditions has the difference of 0.5–2.0%, which shows that the developed model for ozone bleaching of wheat straw pulp is satisfactory.     

Kinetic Models for Peroxide Bleaching Under Alkaline Conditions. I. One and Two Chromophore Models

Several kinetic models for alkaline peroxide bleaching of Eucalypt mechanical pulp have been examined. A previously reported kinetic model, developed to describe peroxide bleaching of softwoods, was found to be inadequate. The models proposed here assume two distinct categories of chromophores which are eliminated through first order processes, rather than the high orders for reaction processes suggested in previous kinetic analyses. Our model enables prediction of a maximum in the rate of bleaching in the range pH 11–12, whereas previous models imply that the rate of chromophore elimination increases continuously with hydroxide ion concentration.     

Removal of Diazinon from aqueous solution by electrocoagulation process using aluminum electrodes

Electrocoagulation (EC) is an electrochemical method to treat polluted wastewaters and aqueous solutions. In this paper, the removal of Diazinon was studied by EC on aluminum electrode. The effect of several parameters such as initial concentration of Diazinon, current density, solution conductivity, effect of pH, and electrolysis time were investigated on EC performance. The obtained results showed that the removal efficiency of EC depends on the current density, initial concentration of Diazinon and electrolysis time. The optimum pH is 3 and also the solution conductivity has no significant effect on removal efficiency.     

废纸脱墨浆H_2O_2漂白的影响因素

研究了脱墨浆过氧化氢漂白特性。研究结果表明 ,脱墨浆采用过氧化氢漂白时 ,过氧化氢的无效分解的程度大。脱墨浆采用过氧化氢漂白时 ,过氧化氢同氢氧化钠用量比为 1∶0 .6,漂白反应时间为 2h ,漂白反应温度为 70℃ ,浆浓为 1 0 %比较合适     

Studies on the influence of chloride ion and pH on the electrochemical behaviour of aluminium alloys 8090 and 2014

The influence of chloride ion concentration and pH (2.0, 6.0 and 11.0) on the corrosion behaviour of 8090 (Al-Li-Cu-Mg-Zr) and 2014 (Al-4.4%Cu) alloys has been studied in NaCl solution using a potentiodynamic polarization technique. The corrosion rate for both the alloys was high at pH values of 2.0 and 11.0 as compared to that at pH 6.0, and the rate increased in chloride ion concentration at all pH levels. A similar result was found for the passive current density. Increase in pH changed the slope of the cathodic polarization curve by changing the cathodic reaction. Increasing the chloride ion concentration decreased the cathodic reaction rate. On the other hand, the anodic reaction rate increased with increase in chloride ion concentration. The open circuit corrosion potential and the pitting potential shifted in the active (negative) direction with increasing pH and chloride ion concentration. The i _p values for 8090-T851 were slightly lower than those for 2014-T6.     

Treatment of Endocrine Disrupting Chemical From Aqueous Solution by Electrocoagulation

The removal of endocrine disrupting chemical (BPA; Bisphenol–A) from aqueous solution was experimentally investigated by electrocoagulation process. The effects of different combinations of aluminum (Al) and iron (Fe) electrode pair, supporting electrolyte type, supporting electrolyte concentration, initial pH and applied current density and initial BPA concentration on the Chemical Oxygen Demand (COD), and energy consumption performances were critically evaluated. The experiment results indicate that Al–Al electrode pair is the most efficient choice of the four electrode pairs. The COD removal efficiency was increased when NaCl was used as the supporting electrolyte instead of Na₂SO₄ and NaNO_3. The optimum supporting electrolyte type and its concentration, initial pH, applied current density and treatment time were found to be NaCl, 0.05 M, pH 7.0, 12 mA cm^?2 and 40 min, respectively. Energy consumption was found to decrease with increase of NaCl concentration while it increases with increasing applied current density. The initial and treated sample was characterized by UV–vis spectroscopy to confirm the treatment efficiency. The sludge formed during electrocoagulation was characterized by XRD and SEM/EDAX analysis.     

Organochlorine Formation in Tertiary Amine Catalyzed Pulp Bleaching

An oxygen delignified eucalyptus kraft pulp was bleached by applying a catalytic amount of a tertiary amine, 1,4-diazabicyclo[2,2,2]octane, and hypochlorous acid at varying pH, temperature, and time. The bleaching filtrate was analyzed for chloroform and AOX and the pulp for residual lignin, hexenuronic acid, and OX. In comparison with chlorine dioxide bleaching, the novel catalytic bleaching (pH < 6) generated only traces of chloroform and low contents of AOX and OX. Separate catalytic oxidations of authentic hexenuronic acid showed that it was a major precursor of chloroform. The results demonstrate a practical way to reduce organochlorine formation in pulp bleaching and provide new understanding on the reaction pathways that yield chloroform.     

电化学降解废水中酚的研究

在氯盐电解质中用电化学方法处理含酚废水，研究了盐的种类、浓度、温度、电流密度、苯酚初始浓度、阴阳极转换频率分别对苯酚去除率、ClO^-浓度及其电流效率的影响当Na2SO4的浓度为0．2mol／L、NaCl的浓度为0．1mol／L、苯酚初始浓度为200mg／L、电流密度为0．04A／cm^2、温度为35℃、pH=12．5、阴阳极转换频率5min／次及反应时间200min的条件下，苯酚的去除率为100％，COD去除率为5％。     

Simulating the impact of kraft pulping and bleaching parameters on Eucalyptus camaldulensis pulp properties using MATLAB

In this work, Eucalyptus camaldulensis was evaluated as the raw material for chemical pulp under different pulping and bleaching conditions. The pulping was carried out at different H‐factors, and at different effective alkalis. The resulting pulps were then oxygen delignified and bleached using various dosages of bleaching chemicals in a D₀EpD₁ sequence. The effect of independent variables (pulping or bleaching variables) on dependent variables (pulp properties) was analysed based on the multivariable least square method via MATLAB software. An agreement was found between the results predicted from the models and the experimental data. To obtain a kappa number of 15, the optimum pulping conditions were a temperature of 155°C, a time of 225 min, and an EA of 23%. Also, the hexenuronic acid (HexA) content of cooked pulp was significantly decreased in the chlorine dioxide bleaching stages, and was only marginally related to the final HexA content of bleached pulps.     

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.     

粉煤灰对活性艳红溶液的吸附脱色处理

以活性艳红染料模拟废水为研究对象,考察粉煤灰对染料废水的吸附脱色作用,考察了粉煤灰的加灰量、吸附时间、吸附温度、废水pH值及初始浓度对活性艳红脱色率的影响。实验表明,废水初始浓度越低,吸附时间越长,脱色效果越好,当吸附时间达60 min时,脱色率趋于稳定;随着粉煤灰加入量的增加,脱色率呈上升趋势,对于100 mg/L的染料溶液,当粉煤灰用量为60 g/L时,染料溶液脱色率可达95%;粉煤灰脱色效果受pH值影响很大,碱性条件下粉煤灰的脱色率较高,酸性条件下次之,中性条件下最差,最佳pH值为10。脱色率随温度的升高而下降,但影响不大。     

电化学氧化降解磺胺嘧啶模拟废水的工艺优化

在无隔膜电解槽中,以NaCl为电解质,利用形稳阳极(DSA)产生的羟基自由基(·OH)和原位电生成的活性氯氧化降解磺胺嘧啶(Sulfadiazine,SD)模拟废水。通过高效液相色谱分析SD及其产物含量变化,水杨酸捕集羟基自由基法测定·OH的浓度,探讨工艺参数对·OH、氯离子、余氯、总氯和总有机碳(TOC)去除率的影响。结果表明,反应10 min后SD去除率达100%,反应4 h后溶液TOC明显下降;反应4 h后,pH=3、4、8、8.5、10和12的反应体系中TOC去除率分别为29%、46%、55%、61%、52%和47%,峰值出现在pH=8.5时;提高电流密度、电解质NaCl浓度及降低SD初始质量浓度可增大TOC去除率。该实验最优工艺条件为:pH=8.5,外加NaCl 0.025 mol/L,电流密度20 mA/cm2,初始质量浓度100 mg/L SD,经4 h的电化学氧化降解,TOC去除率达到66%。