Geography Vocabulary - Native Lily Ragauskas Rishkat Khan Vanessa Xavier.
Chemistry of Chlorine Dioxide Pulp Bleaching - UT KnoxvilleChemistry of Chlorine Dioxide Pulp...
39
Transcript of Chemistry of Chlorine Dioxide Pulp Bleaching - UT KnoxvilleChemistry of Chlorine Dioxide Pulp...
Bleaching History
• Bleach - 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 acid from sour milk– Became known as “grass bleaching”– Perfected around Haarlem, Holland– Material generally of linen fibers
Bleaching History• 1756 – Francis Home (Scotland)
– Discovered that by substituting dilute sulfuric acid for lactic acid in last step, operating time is reduced.
– Still is a grass bleaching operation and not used yet for paper – “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)
Bleaching History
• Thomas Henry – English – extended use of bleaching solution to paper (rag)
• 1798 – Charles Tennant – Scotland – formulated calcium hypochlorite by reaction of
chlorine gas 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
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
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
Chlorine Dioxide• Molecular Weight: 67.45• Boiling Point: 11°C• Yellow green to orange
gas, with a sharp pungent odor
• Water soluble, 10 g/L• Oxidant• Density: 2.4 x’s water• Decomposes to Cl2 and O2
with noise, heat, flame, and minor pressure wave
Formation of Chlorine Dioxide
• Reduction of chlorate in acidic medium: – ClO3
- + 2 H+ + e- ClO2 + H2O
• Oxidation of chlorite ion: – ClO2
- ClO2 + e-
Reductive Chemistry
• Reducing agents are used to make the e-
– SO2 + 2 H2O SO42- + 4 H+ + 2 e-
– CH3OH + H2O HCOOH + 4 H+ + 4 e-
– Cl- ½ Cl2 + e-
– H2O2 O2 + 2 H+ + 2 e-
Making Chlorine Dioxide
• 2 ClO3- + SO2 2 ClO2 + SO4
2-
• 4 ClO3- + CH3OH + 4 H+ 4 ClO2 +
HCOOH + 3 H2O• ClO3
- + Cl- + 2 H+ ClO2 + Cl2 + H2O• 2 ClO3
- + H2O2 + 2 H+ 2 ClO2 + O2 + 2 H2O
• ClO3- + 6 H+ + 6e- Cl- + 3 H2O
Chlorine Dioxide
Chemical properties:
One of several known oxides of chlorine.
Chlorine dioxide is a powerful oxidizing agent - 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.
Chlorine Dioxide
How long has chlorine dioxide been used? Chlorine dioxide has found widespread use since the early 1950s in the treatment of drinking water 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.
Chlorine Dioxide
• Food industryFruit and vegetable washingMeat and poultry disinfectionSanitizing food process equipment
• Medical“Tristel” sterilizing solutions for medical instrumentsAir disinfection and building decontamination. (2001 anthrax attacks, US)
• Personal hygieneMouthwashes (~0.003%)ToothpastesContact lens cleaners
• Other industryCooling systems and towers in the control of Legionella.(Gram negative bacterium)
Chlorine dioxide has many applications:
Bleaching Pulp with Chlorine Dioxide
Advantages
High brightness and brightness stabilityExcellent for shive and dirt removal - the bestHighly selective - little degradation of pulpLess organic chlorine than Cl2 and ClO-
Radical scavenger
Bleaching Pulp with Chlorine DioxideDisadvantages
Highly explosive – hence generate on-siteHighly corrosive - need titanium equipment -high capital costExpensiveToxic - handle with careAOXChlorate formation
26-40% loss in oxidation power
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%
Chlorine Dioxide Puffs
• Puff – deompostion of chlorine dioxide– 2 ClO2 Cl2 + 2 O2 + heat– Low speed wave of reaction (< 1m/s)
• Explosion: > 300 m/s
– Generators designed for up to 200 mm Hg
AOX vs. ClO2 Substitution
012345678
0 20 40 60 80 100
ClO2 Substitution, %
AO
X, k
g/ad
mt
Unbl 30EO 23.5EOP 20.5O 16.6
Kappa
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 = 35.5ClO2 + 5e- = Cl- ⇒ 67.5/5 = 13.5
35.5 / 13.5 = 2.63
Chloroform – CHCl3
00.05
0.10.15
0.20.25
0.30.35
0 0.1 0.2 0.3 0.4
Chlorine Factor
Chl
orof
orm
, kg/
odm
t
100%71%46%28%0%
% ClO2 sub
Substitution of Chlorine Dioxide for Chlorine
Old Bleaching Sequences:(CD)E1D1E2D2 O (CD)E1D1E2D2
ECF Sequences:D0E1D1E2D2 O D0E1D1E2D2
ECF = Elemental Chlorine-Free
Chlorine Dioxide
• ChemistryClO2 + e-⇒ ClO2
-
ClO2- + 3H+ + 2e-⇒ HClO + H2O
HClO + H+ + 2e- ⇒ Cl- + H2O ClO2 + 4H+ + 5e- ⇒ Cl- + 2H2O
Equivalent Weight: ClO2 = 67.5/5 = 13.5Cl2 = 71/2 = 35.5
Basic Cation Radical Mechanism of Chlorine Dioxide
R = Alkyl or R2
R1 = H, Alkyl or Aryl CT - Complex
π-Complex
Non-phenolic structures Phenolic structures
OR1
OCH3
R
ClO2
OOCH3
R
+ H+
- HClO2
R1 = Alkyl or arylR1 = H
R
OR1
OCH3
ClO2
R
OR1
OCH3
R
OR1
OCH3
+
R
OR1
OCH3+
R
OHOCH3
+
Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991)
- HClO2
O
H3CCOOCH3
OCH3O
- HClO2
- HOCl
CH3
OOCH3O
Dimers and polymers
O
H3CCOOCH3
O
- HOCl
+ H2O
CO2CH3
CH3
CO2H
+ H2O
- HOCl
+ HClO2
OHOCH3
CHO
OHOCH3
CH2OH
OHOCH3
H2C OClO-
OHOCH3
OHCH3O
CH3
CH2
OOCH3
ClO2 ClO2CH3
OOCH3
-OClOCH3
OOCH3
H-OClO
ClO2
+ H2O
- CH3OH
CH3
O OCH3
OClO-
CH3
OO
CH3
OOCH3
CH3
OOCH3
CH3
OOCH3
CH3
OOCH3
+ H2O
- HOCl
Bicreosol
Basic Phenolic Compound Reactions
Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991)
Basic Non-Phenolic Compound ReactionsCH3
OCH3
OCH3
+
CH3
OCH3
OCH3+
CH3
OCH3
OCH3H
+
CH3
OCH3CH3O+
CH3
OCH3
OCH3
H
+
CH3
OCH3
OCH3
+
CH3
OCH3
OCH3H
-OClO+
CH3
OCH3
OCH3
H-OClO +
ClO2ClO2 ClO2
ClO2
CH3
OCH3
O
O
+ H2O
- HOCl- H+
+
CH3
OCH3CH3O OClO-
CH3
OCH3
OCH3
O
- CH3OH - CH3OH
- H+- HOCl
+ H2O+ H2O- HClO2- H+- CH3OH
+ H2O- HOCl
CH3
HO HO
CO2CH3
CH3
OCH3
OCH3
-OClO
+
CO2CH3
CH3
CO2CH3
CH3
OCH3
OCH3
ClO2
ClO2
ClO2 ++ ClO2
Brage, Ericksson and Gierer, Holzforschung, 45(1):23 (1991)
0
20
40
60
80
100
0 50 100 150Reaction Time (min.)
Perc
ent C
ompo
und
I
pH 2pH 4pH6pH 8
ClO2 Oxidation of Methylveratrylalcohol
Effect of pH on Rate of Reaction
O
O
H3C
OCH3
O
OCH3
OCH3
CHHO CH3
Cl
OCH3
OCH3
OH3C
OCH3
OCH3
Cl
Cl
CHCH3HO
OCH3
OCH3
O
O
OCH3
3 5 6
8 9 10
Effect of pH on the Reaction of ClO2 with Methylveratrylalcohol (MVA)
OCH3
OCH3
CH3HO
MVA
Gunnarsson and Ljunggren, Acta Chem. Scand., 50: 442 (1996)
Effect of End pH in a D1 Stage on Brightness and Chlorite and Chlorate Formation
6668707274767880828486
2 3 5 7 8 10End pH in the D1 stage
Brig
htne
ss, %
ClO2-ClO3-ClO3- + ClO2-Brightness
1.81.6
1.4
1.2
1.00.80.60.40.2
Chlorate and/orchlorite, % ofavailable chlorine on pulp
Rapson, H., and C.B Anderson, Tappi, 61 (10):97 (1978)
0.0
1.0
2.0
3.0
4.0
5.0
0 2 4 6 8 10 12
End pH
Con
cent
ratio
n (m
M)
ChloriteChlorate
Kappa no. 10.7, kappa factor 0.20, pulp consistency, 3.5%, 60oC, 60 min
Effect of pH on ClO3- and ClO2
- formation in ClO2prebleaching of oxygen delignified kraft pulp
Wang, L. J. and B. H. Yoon, Paper presented at the International symposium on Cellulose 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
6668707274767880828486
2 3 5 7 8 10End pH in the D1 stage
Brig
htne
ss, %
ClO2-ClO3-ClO3- + ClO2-Brightness
1.81.6
1.4
1.2
1.00.80.60.40.2
Chlorate and/orchlorite, % ofavailable chlorine on pulp
Rapson, H., and C.B Anderson, Tappi, 61 (10):97 (1978)
2ClO2 + HOCl + H2O 2ClO3- + HCl + 2H+ (4)
ClO2 + Free Radical + H2O ClO3- (1)
2ClO2 + HO- HClO2 + ClO3
- (2)
HClO2 + ClO2- HOCl + ClO3
- (3)
ClO2- + HOCl + H2O* *ClO3
- + HCl + H2O (5)
Chlorate Forming Reactions
pK1~ 1.8 pK2 ~ 7.5Cl2 + H2O ClO- + H+K1 K2
H + Cl + ClOH
H C lO 2 C lO 2- + H +
p K a ~ 2 .3
Dissociation Constants of Hypochlorousand Chlorous acids
-d(ClO2-)/dt = k1(HClO2)2 + k2(ClO2
-)(HClO2)
HClO2 ClO2- + H+
pKa~2.3
HClO2 + Cl- + H+ 2HOCl (7)Fast
HClO2 + ClO2- HOCl + ClO3
- (3) Slow
Disproportionation of Chlorous Acid
Kieffer andGordon, Inorganic Chem., 7(2):239 (1968)
Hong and Rapson, Canadian J. Chem., 46:2053 (1968)
ClO2- + HOCl Cl Cl
O
O-HO-
ClO2- 2ClO2 + Cl- (6)
H2O
ClO3- + HCl + H+ (5)
Oxidized Lignin + Cl-/ 2Cl-
Lignin + ClOH/Cl2
Organic-Cl + H2O/ Cl-
Competitive Reactions of Hypochlorous Acid
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.
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 chlorinedioxide.• Lactones, muconic acid esters, maleic acid, oxiranes and quinoidstructures are the dominant oxidation products along with significant levels of methanol.• Chlorinated organics are produced during ClO2 bleaching, primarily due to the in situ formation of hypochlorous acid.
