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Home , Chlorine dioxide, Elemental chlorine free

Chemistry of Dioxide Bleaching

[email protected] Bleaching History

• - blecan (Anglo Saxon) – to fade • First dates back to ancient Gauls: sunlight on vegetable fibers moistened with alkaline solution from wood or vegetable ash • Process: alkali treatment, exposure on grassy meadows to sun, washing, repeat, final treatment with lactic from sour milk – Became known as “grass bleaching” – Perfected around Haarlem, Holland – Material generally of linen fibers

[email protected] Bleaching History

• 1756 – Francis Home (Scotland) – Discovered that by substituting dilute for lactic acid in last step, operating time is reduced. – Still is a grass bleaching operation and not used yet for – “White” paper made from sorted white rags • 1774 – Karl Wilhelm Scheele (Swedish Chemist) – discovered chlorine and pioneered use as a bleaching chemical on vegetable fibers • Berthollet – French chemist – discovered chlorine could be absorbed in solution of caustic potash and resulting solution had efficient bleaching action with less degrading effect on the finished goods (product)

[email protected] Bleaching History

• Thomas Henry – English – extended use of bleaching solution to paper (rag) • 1798 – Charles Tennant – Scotland – formulated by reaction of chlorine with milk of lime • 1799 – Charles Tennant – patent on production of bleaching powder by action of chlorine on slaked lime – became world’s most dominant bleaching agent

[email protected] Bleaching History

• 1920’s: Continuous operating bleaching introduced by Thorne in multi-stage bleaching – for purification of pulp from demand for large tonnages of nitrocellulose during WWI – 2 stage hypochlorite then added alkaline extraction in between hypochlorite stages • Use of Chlorine dioxide investigated from 1920 – 1940, put into production 1940’s

[email protected] Chlorine Dioxide History

• 1946 – 1980’s used as a later bleaching stage, not for delignification – CEHDED, CEDED

• Late 1980’s realized that ClO2 and Cl2 used together had a higher delignification efficiency than Cl2 alone • Environmental regulations dictated the switch from elemental chlorine (Cl2 & HOCl) to ClO2 and other TCF methods

[email protected] Chlorine Dioxide

• Molecular Weight: 67.45 • : 11°C • Yellow green to orange gas, with a sharp pungent • Water soluble, 10 g/L • Oxidant • : 2.4 x’s water

• Decomposes to Cl2 and O2 with noise, heat, flame, and minor pressure wave

[email protected] Formation of Chlorine Dioxide

• Reduction of chlorate in acidic medium: - + - –ClO3 + 2 H + e Æ ClO2 + H2O

• Oxidation of ion: - - –ClO2 Æ ClO2 + e

[email protected] Reductive Chemistry

• Reducing agents are used to make the e- 2- + - –SO2 + 2 H2O Æ SO4 + 4 H + 2 e + - –CH3OH + H2O Æ HCOOH + 4 H + 4 e - - –Cl Æ ½Cl2 + e + - –H2O2 Æ O2 + 2 H + 2 e

[email protected] Making Chlorine Dioxide

- 2- •2 ClO3 + SO2 Æ 2 ClO2 + SO4 - + •4 ClO3 + CH3OH + 4 H Æ 4 ClO2 + HCOOH + 3 H2O - - + •ClO3 + Cl + 2 H Æ ClO2 + Cl2 + H2O - + •2 ClO3 + H2O2 + 2 H Æ 2 ClO2 + O2 +

2 H2O - + - - •ClO3 + 6 H + 6e Æ Cl + 3 H2O

[email protected] Chlorine Dioxide

Chemical properties:

One of several known of chlorine. Chlorine dioxide is a powerful - an electron receiver. This means that the chlorine dioxide molecule is in constant search for an additional electron. → Disinfection The destruction of pathogenic and other kinds of microorganisms by physical or chemical means

When a bacterial cell comes into contact with chlorine dioxide it donates an electron from its cell wall, thereby creating a breach in the cell wall through which cell contents pass in an attempt to bring the concentrations on either side of the cell membrane to equilibrium. The cell dies through lysis.

[email protected] Chlorine Dioxide

How long has chlorine dioxide been used?

Chlorine dioxide has found widespread use since the early 1950s in the treatment of and swimming pools.

Today, chlorine dioxide is used by many large cities in Europe, such as (1956) Brussels, Zurich, Düsseldorf, Toulouse and Vienna, to sanitize the drinking water supply.

[email protected] Chlorine Dioxide

Chlorine dioxide has many applications:

• Food industry Fruit and vegetable washing Meat and poultry disinfection Sanitizing food process equipment

• Medical “Tristel” sterilizing solutions for medical instruments Air disinfection and building decontamination. (2001 attacks, US)

• Personal hygiene Mouthwashes (~0.003%) Toothpastes Contact lens cleaners

• Other industry Cooling systems and towers in the control of .(Gram negative bacterium)

[email protected] Bleaching Pulp with Chlorine Dioxide Advantages

¾High brightness and brightness stability ¾Excellent for and dirt removal - the best ¾Highly selective - little degradation of pulp - ¾Less organic chlorine than Cl2 and ClO ¾ scavenger

[email protected] Bleaching Pulp with Chlorine Dioxide Disadvantages

¾ Highly explosive – hence generate on-site ¾ Highly corrosive - need equipment - high capital cost ¾ Expensive ¾ Toxic - handle with care ¾ AOX ¾ Chlorate formation ¾ 26-40% loss in oxidation power [email protected] ClO2 Delignification Process Conditions

• Total Chemical Charge: 0.15 – 0.25 kappa factor • Chlorine dioxide charge: 25 – 100% of the total • Temperature: 30 -60° C • Total Time: 20 – 60 minutes • End pH: 1.5 – 3 • Consistency: 3 – 4%

[email protected] Chlorine Dioxide Puffs

• Puff – deompostion of chlorine dioxide

–2 ClO2 Æ Cl2 + 2 O2 + heat – Low speed wave of reaction (< 1m/s) • Explosion: > 300 m/s

– Generators designed for up to 200 mm Hg

[email protected] AOX vs. ClO2 Substitution

8 7 Kappa 6 5 Unbl 30 EO 23.5 4 EOP 20.5 3 O 16.6 2 AOX, kg/admt AOX, 1 0 0 20406080100 ClO2 Substitution, % [email protected] Liebergott Substitution of Chlorine Dioxide

• AOX Generation

– AOX (kg/t) = 0.1 (Cl2, kg/t active chemical)

– AOX (kg/t) = 0.1(1/2.63)(.526)(ClO2, kg/t active chemical)

0.02(ClO2, kg/t act chemical)

• On an equal weight basis ClO2 is 2.63 times as as reactive as Cl2 - - Cl2 + 2e = 2Cl ⇒ 71/2 = 35.5 - - ClO2 + 5e = Cl ⇒ 67.5/5 = 13.5 35.5 / 13.5 = 2.63

[email protected] Chloroform – CHCl3

0.35 % ClO2 sub 0.3 100% 0.25 71% 0.2 46% 0.15 28% 0.1 0% 0.05

Chloroform, kg/odmt 0 0 0.1 0.2 0.3 0.4 Chlorine Factor

[email protected] Effect of Chlorine Multiple on Dioxin Formation

[email protected] Substitution of Chlorine Dioxide for Chlorine

Old Bleaching Sequences:

(CD)E1D1E2D2 O (CD)E1D1E2D2

ECF Sequences:

D0E1D1E2D2 O D0E1D1E2D2

ECF = Elemental Chlorine-Free

[email protected] Chlorine Dioxide

O Cl O O Cl O O Cl O

[email protected] Chlorine Dioxide

• Chemistry - - ClO2 + e ⇒ ClO2 - + - ClO2 + 3H + 2e ⇒ HClO + H2O + - - HClO + H + 2e ⇒ Cl + H2O + - - ClO2 + 4H + 5e ⇒ Cl + 2H2O

Equivalent Weight: ClO2 = 67.5/5 = 13.5

Cl2 = 71/2 = 35.5

[email protected] Basic Cation Radical Mechanism of Chlorine Dioxide

R

OCH3 O R1

ClO2

R = Alkyl or R2 R R1 = H, Alkyl or Aryl ClO 2 CT - Complex OCH3 π-Complex O R1 + H+ - HClO2

R R1 = Alkyl R R R R = H R 1 or aryl

OCH3 OCH3 OCH3 OCH3 OCH3 + O + OH O O+ O R1 R1 R1 Phenolic structures Non-phenolic structures

Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991) [email protected] Basic Phenolic Compound Reactions

CH3

OCH3 O

CH3 CH3 - CH3 OClO CH3 ClO2 ClO2 H OCH OCH OCH -OClO OCH3 3 3 3 O O O O + H2O - HClO2 - HOCl - HOCl CH3 CH3 H3C COOCH3 CH2 O CH3 Bicreosol OCH3 CH3O CH O 3 O OH O OCH3 O OCH3 O OCH3 ClO2 + HClO2 O + H2O OH - CH3 H2C OClO CH2OH CH3 - HClO 2 OClO- + H2O OCH OCH3 O OCH3 3 - CH3OH O OH O OH Dimers + H2O - HOCl and polymers - HOCl

H3C CH3 COOCH3 CHO O CO2CH3 O CO2H OCH3 OH Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991)

[email protected] Basic Non-Phenolic Compound Reactions

CH3 CH3 ClO2 ClO2 CH3

+ ClO2 ClO2 + OCH3 + OCH3 OCH3 OCH3 + OCH3 OCH3

CH3 CH CH CH3 H 3 3 H + + OCH3 OCH 3 OCH3 OCH3 + OCH3 CH3O + OCH3 OCH3

ClO2 ClO2 ClO2 ClO2

CH - 3 OClO CH3 CH CH3 H 3 - H OClO + - OCH OCH3 + OClO 3 OCH OCH3 OCH 3 CH3O - + OCH3 + 3 OClO OCH3 + H O 2 + H2O + H2O + H2O - HOCl - HClO2 - CH3OH - CH3OH + - CH3OH - H - HOCl - HOCl + - H - H+ CH3 O CH 3 CH 3 CH3 O O HO H CO CH OCH3 2 3 CO2CH3 OCH3 O CO CH OCH3 2 3 [email protected] Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991) ClO2 Oxidation of Methylveratrylalcohol Effect of pH on Rate of Reaction

100

80 pH 2 60 pH 4 pH6 40 pH 8 20 Percent Compound I 0 050100150 Reaction Time (min.)

[email protected] Effect of pH on the Reaction of ClO2 with Methylveratrylalcohol (MVA)

HO CH3

MVA OCH3

OCH3

O H3C O O OCH3

H3C

OCH3 OCH3 O O OCH 3 O 3 5 6

HO CH3 HO CH3 CH CH Cl Cl

Cl OCH3 OCH3 OCH3

Gunnarsson and Ljunggren, Acta Chem. Scand., 50: 442 (1996) OCH3 OCH3 OCH3 8 9 10 [email protected] Effect of End pH in a D1 Stage on Brightness and Chlorite and Chlorate Formation Rapson, H., and C.B Anderson, Tappi, 61 (10):97 (1978) 86 ClO2- ClO3- 84 1.8 ClO3- + ClO2- 1.6 82 Brightness 80 1.4 78 1.2 76 1.0 Chlorate and/or chlorite, % of 74 0.8 available chlorine

Brightness, % Brightness, 0.6 72 on pulp 70 0.4 0.2 68 66 2357810

End pH in the D1 stage

[email protected] - - Effect of pH on ClO3 and ClO2 formation in ClO2 prebleaching of delignified kraft pulp

5.0

4.0

3.0 Chlorite Chlorate 2.0

1.0 Concentration (mM) 0.0 0 2 4 6 8 10 12 End pH

Kappa no. 10.7, kappa factor 0.20, pulp consistency, 3.5%, 60oC, 60 min Wang, L. J. and B. H. Yoon, [email protected] presented at the International symposium on and Lignocellulosics Chemistry 2000, Dec. 16-18, 2000, Kunming, China Effect of End pH in a D1 Stage on Brightness and Chlorite and Chlorate Formation Rapson, H., and C.B Anderson, Tappi, 61 (10):97 (1978) 86 ClO2- ClO3- 84 1.8 ClO3- + ClO2- 1.6 82 Brightness 80 1.4 78 1.2 76 1.0 Chlorate and/or chlorite, % of 74 0.8 available chlorine

Brightness, % Brightness, 0.6 72 on pulp 70 0.4 0.2 68 66 2357810

End pH in the D1 stage

[email protected] Chlorate Forming Reactions

- ClO2 + Free Radical + H2O ClO3 (1)

- - 2ClO2 + HO HClO2 + ClO3 (2) - - HClO2 + ClO2 HOCl + ClO3 (3) - + 2ClO2 + HOCl + H2O 2ClO3 + HCl + 2H (4)

- - ClO2 + HOCl + H2O* *ClO3 + HCl + H2O (5)

[email protected] Dissociation Constants of Hypochlorous and Chlorous

- + HClO2 ClO2 + H pKa~2.3

K 1 K2 - + Cl2 + H2O H + Cl + ClOH ClO + H pK1~ 1.8 pK2 ~ 7.5

[email protected] Disproportionation of

- Slow - HClO2 + ClO2 HOCl + ClO3 (3)

- 2 - -d(ClO2 )/dt = k1(HClO2) + k2(ClO2 )(HClO2)

pKa~2.3 - + HClO2 ClO2 + H

- + Fast HClO2 + Cl + H 2HOCl (7) Kieffer andGordon, Inorganic Chem., 7(2):239 (1968) Hong and Rapson, Canadian J. Chem., 46:2053 (1968)

[email protected] Competitive Reactions of

- - 2ClO2 + Cl (6) O ClO2 - ClO2 + HOCl Cl Cl H O -HO- 2 O - + ClO3 + HCl + H (5)

Oxidized + Cl-/ 2Cl-

Lignin + ClOH/Cl2 - Organic-Cl + H2O/ Cl

[email protected] Summary

•In D0, the increase in chlorate and bleaching efficiency levels off at end pH below 3.4, whereas AOX continues to increase with decreasing pH.

•In D0, the phenolic hydroxyl content of lignin in pulp has little effect on either chlorate formation or bleaching efficiency.

[email protected] Summary

• The phenolic lignin structures have demonstrated enhanced reactivity with chlorine dioxide over that of the non-phenolic units.

• The initial stage of ClO2 delignification is believed to be the abstraction of an electron from the phenolate anion followed by further degradation caused by additional equivalents of chlorine dioxide. • Lactones, muconic acid esters, maleic acid, oxiranes and quinoid structures are the dominant oxidation products along with significant levels of . • Chlorinated organics are produced during ClO2 bleaching, primarily due to the in situ formation of hypochlorous acid.

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