Mechanism of formation of chloro-organics during chlorine dioxide prebleaching of kraft pulp

Ni, Yonghao; Heiningen, A. R. P. Van; Kubes, G. J.

doi:10.3183/npprj-1993-08-04-p350-351

Cited by 10 publications

(10 citation statements)

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“…Intermediates of XClO 2 (where X = Cl, Br, or I) have been proposed as transient species in chlorite ion reactions with molecular chlorine, bromine, or iodine, as well as with hypohalous acids (HOX, where X = Cl or Br). − Taube and Dodgen 1 were the first investigators to propose a metastable intermediate, Cl 2 O 2 , in the reactions of ClO 2 - with Cl 2 or HOCl. Their tracer experiments with radioactive chlorine gave unlabeled ClO 2 and ClO 3 - as products along with labeled Cl - .…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

1998

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The rate of oxidation of ClO(2)(-) by HOBr is first-order in each reactant and is general-acid-assisted in the presence of phosphate or carbonate buffers. The products are ClO(2) and ClO(3)(-), where the relative yield depends on the concentration ratio of ClO(2)(-)/OH(-). The kinetic dependence indicates the presence of a steady-state intermediate, HOBrOClO(-) (or HOBrClO(2)(-)), that undergoes general-acid-assisted reactions to generate a metastable intermediate, BrOClO (or BrClO(2)). This intermediate reacts very rapidly by two competing pathways: in one path ClO(2)(-) reacts to form 2ClO(2) and Br(-), and in the other path OH(-) (or H(2)O) reacts to form ClO(3)(-) and Br(-). Competition between these pathways determines the yield of ClO(2) but does not affect the rate of loss of HOBr. The reactions are followed by the formation of ClO(2) in the presence of excess ClO(2)(-). The rate expression for the loss of HOBr is k(1)[ClO(2)(-)][HOBr] summation operator(k(HA)[HA])/(k(-)(1) + summation operator(k(HA)[HA])), where k(1) (for the formation of the intermediate) is 97 M(-)(1) s(-)(1) and k(HA)/k(-)(1) (M(-)(1)) values, which depend on the acid (HA) strength, are 3.1 x 10(5) for H(3)O(+), 8.3 for H(2)PO(4)(-), and 0.064 for HCO(3)(-) (25.0 degrees C, &mgr; = 1.0 M). Reactions between HOBr and ClO(2)(-) are much faster than those between HOCl and ClO(2)(-).

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Section: Introductionmentioning

confidence: 99%

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

1998

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“…However, even pure chlorine dioxide bleaching still leads to the formation of organically bound chlorine due to the fact that hypochlorous acid is generated in situ as a reaction intermediate during the course of reactions (Kolar et al, 1983;Ni et al, 1992). In an earlier paper (Ni et al, 1993), it was found that the formation of organically bound chlorine during CIO, prebleaching of Kraft pulp was due to the reaction between lignin and in-situ hypochlorous acid. In addition, the consumption of hypochlorous acid is competing in a reaction with chlorite, another reaction intermediate formed during chlorine dioxide bleaching.…”

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confidence: 98%

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

Wang

1997

Can J Chem Eng

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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.

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“…This model serves to illustrate why oxidations using ClO 2 alone often display relatively poor selectivity, and it is also a likely reason that industrial bleaching with ClO 2 is often accompanied by chlorination side reactions. [27][28][29]69,82 Epoxide Yield As a Function of Chlorite and Initial Chlorine Dioxide Concentrations. A useful quantitative mechanism allows calculation of product yield as a function of the initial reaction conditions.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Over the last 30 years, chlorine dioxide has largely replaced chlorine as the dominant agent for the bleaching of wood pulp because of its lower tendency to form chlorinated products in the oxidation of organic compounds, ,, significantly reducing the release of organochlorine pollutants into the environment. Several studies − concerning the reactions in “ClO 2 only” (elemental chlorine free (ECF)) pulp bleaching have shown that hypochlorous acid is produced as a byproduct of the reaction with lignin, and HOCl is now considered to be responsible for chlorination products in ECF pulp bleaching, although at a much-reduced level compared to traditional chlorine bleaching. Conjugated C–C double bonds are a common feature of organic chromophores in natural pigments in textiles and wood pulp, so the present work contributes to an improved understanding of that complex oxidative chemistry.…”

Section: Introductionmentioning

confidence: 99%

Kinetics and Mechanism of Styrene Epoxidation by Chlorite: Role of Chlorine Dioxide

2014

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An investigation of the kinetics and mechanism for epoxidation of styrene and para-substituted styrenes by chlorite at 25 °C in the pH range of 5-6 is described. The proposed mechanism in water and water/acetonitrile includes seven oxidation states of chlorine (-I, 0, I, II, III, IV, and V) to account for the observed kinetics and product distributions. The model provides an unusually detailed quantitative mechanism for the complex reactions that occur in mixtures of chlorine species and organic substrates, particularly when the strong oxidant chlorite is employed. Kinetic control of the reaction is achieved by the addition of chlorine dioxide to the reaction mixture, thereby eliminating a substantial induction period observed when chlorite is used alone. The epoxidation agent is identified as chlorine dioxide, which is continually formed by the reaction of chlorite with hypochlorous acid that results from ClO produced by the epoxidation reaction. The overall stoichiometry is the result of two competing chain reactions in which the reactive intermediate ClO reacts with either chlorine dioxide or chlorite ion to produce hypochlorous acid and chlorate or chloride, respectively. At high chlorite ion concentrations, HOCl is rapidly eliminated by reaction with chlorite, minimizing side reactions between HOCl and Cl2 with the starting material. Epoxide selectivity (>90% under optimal conditions) is accurately predicted by the kinetic model. The model rate constant for direct reaction of styrene with ClO2(aq) to produce epoxide is (1.16 ± 0.07) × 10(-2) M(-1) s(-1) for 60:40 water/acetonitrile with 0.20 M acetate buffer. Rate constants for para substituted styrenes (R = -SO3(-), -OMe, -Me, -Cl, -H, and -NO2) with ClO2 were determined. The results support the radical addition/elimination mechanism originally proposed by Kolar and Lindgren to account for the formation of styrene oxide in the reaction of styrene with chlorine dioxide.

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Mechanism of formation of chloro-organics during chlorine dioxide prebleaching of kraft pulp

Cited by 10 publications

References 0 publications

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

Mechanism of Chlorine Dioxide and Chlorate Ion Formation from the Reaction of Hypobromous Acid and Chlorite Ion

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

Kinetics and Mechanism of Styrene Epoxidation by Chlorite: Role of Chlorine Dioxide

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