Pulping and Bleaching PSE 476: Lecture 181 Pulping and Bleaching PSE 476/Chem E 471 Lecture #18 Bleaching Fundamentals and Bleaching Sequences Lecture #18 Bleaching Fundamentals and Bleaching Sequences

Pulping and Bleaching PSE 476: Lecture 182 Bleaching Sequences Agenda Bleaching chemistry fundamentals »Cationic mechanisms »Radical mechanisms »Anionic mechanisms Bleaching chemicals nomenclature rules Bleaching Conditions Typical Sequences Bleaching chemistry fundamentals »Cationic mechanisms »Radical mechanisms »Anionic mechanisms Bleaching chemicals nomenclature rules Bleaching Conditions Typical Sequences

Pulping and Bleaching PSE 476: Lecture 183 Bleaching: Basic Chemical Principles Bleaching reactions can be divided into anionic, cationic (?) and radical reactions. There are a multitude of different reactions that occur during bleaching. We are going to cover the chemistry in very generic terms. Bleaching reactions can be divided into anionic, cationic (?) and radical reactions. There are a multitude of different reactions that occur during bleaching. We are going to cover the chemistry in very generic terms.

Pulping and Bleaching PSE 476: Lecture 184 Bleaching Mechanisms Joseph Gierer, a well known lignin chemist, has taken the very complicated bleaching reactions and classified them by a number of different categories.

Pulping and Bleaching PSE 476: Lecture 185 Cationic Reactions Cationic reactions occur under acidic conditions. Reactive species: »Chlorine: Cl + »Peroxy acids: OH + »Ozone: O 3 How can these species be cations??????? »Electrophillic addition reaction: Cationic reactions occur under acidic conditions. Reactive species: »Chlorine: Cl + »Peroxy acids: OH + »Ozone: O 3 How can these species be cations??????? »Electrophillic addition reaction:

Pulping and Bleaching PSE 476: Lecture 186 Cationic Reactions: Generalities (2) The most important reaction is electophillic substitution onto the aromatic ring. »There can be multiple substitutions. »Substitution at #1 ring position can later cause side chain elimination. »Substitution at #3 or #4 position can lead to the formation of an ortho quinone. »There is no ring cleavage. The most important reaction is electophillic substitution onto the aromatic ring. »There can be multiple substitutions. »Substitution at #1 ring position can later cause side chain elimination. »Substitution at #3 or #4 position can lead to the formation of an ortho quinone. »There is no ring cleavage.

Pulping and Bleaching PSE 476: Lecture 187 Radical Reactions: Generalities Nobody adds free radicals to a bleaching reaction; they are formed from other additives. Examples: »Chlorine: Cl (chlorine radical) »Oxygen: - O 2 (superoxide radical) HO (hydroxyl radical) Many free radicals react very rapidly with lignin so they are good except that they degrade carbohydrates very rapidly so they are also bad. Nobody adds free radicals to a bleaching reaction; they are formed from other additives. Examples: »Chlorine: Cl (chlorine radical) »Oxygen: - O 2 (superoxide radical) HO (hydroxyl radical) Many free radicals react very rapidly with lignin so they are good except that they degrade carbohydrates very rapidly so they are also bad.

Pulping and Bleaching PSE 476: Lecture 188 Radical Reactions: Generalities (2) Pathways are pH dependent. Free radicals couple with aromatic rings. »This and further mechanisms affected by free versus etherified phenolic hydroxyls. »Results in generation of free radical structures. These structures can undergo additional substitutions and oxidation reactions. »Generation of ortho quinones. »Ring opening reactions. »Ring substitution by bleaching agent. »Some side chain cleavage. Carbohydrates will react and are degraded. Pathways are pH dependent. Free radicals couple with aromatic rings. »This and further mechanisms affected by free versus etherified phenolic hydroxyls. »Results in generation of free radical structures. These structures can undergo additional substitutions and oxidation reactions. »Generation of ortho quinones. »Ring opening reactions. »Ring substitution by bleaching agent. »Some side chain cleavage. Carbohydrates will react and are degraded.

Pulping and Bleaching PSE 476: Lecture 189 Radical Reactions: Generalities Ring Cleavage Ortho Quinones Ring Substitution Side Chain Cleavage

Pulping and Bleaching PSE 476: Lecture 1810 Anionic Reactions: Generalities These are alkaline bleaching reactions. ClO -, HOO - added reagents »Other species generated:. O 2 -,. O -, etc. »These chemicals are involved in nucleophilic attacks. Target of attacks: carbonyls and conjugated carbonyls. Products of reactions: »Ring opening: Dicarboxylic acids »Side chain cleavage These are alkaline bleaching reactions. ClO -, HOO - added reagents »Other species generated:. O 2 -,. O -, etc. »These chemicals are involved in nucleophilic attacks. Target of attacks: carbonyls and conjugated carbonyls. Products of reactions: »Ring opening: Dicarboxylic acids »Side chain cleavage

Pulping and Bleaching PSE 476: Lecture 1811 Anionic Reactions: Generalities

Pulping and Bleaching PSE 476: Lecture 1812 Bleaching Sequences Nomenclature Rules (1) Nomenclature rules found in TAPPI Information Sheet TIS Bleaching sequences are described by capital letters which describe the chemicals used. »C = chlorine, H = hypochlorite, D = chlorine dioxide, O = oxygen (with NaOH), P = peroxide, Z = ozone, Y = hydrosulfite, X = enzymes, E = NaOH, Q = chelants, Paa = peracetic acid Letter represents each chemical followed by a washing step. »CED = Cl 2 /wash/NaOH extraction/wash/ ClO 2 /wash Nomenclature rules found in TAPPI Information Sheet TIS Bleaching sequences are described by capital letters which describe the chemicals used. »C = chlorine, H = hypochlorite, D = chlorine dioxide, O = oxygen (with NaOH), P = peroxide, Z = ozone, Y = hydrosulfite, X = enzymes, E = NaOH, Q = chelants, Paa = peracetic acid Letter represents each chemical followed by a washing step. »CED = Cl 2 /wash/NaOH extraction/wash/ ClO 2 /wash

Pulping and Bleaching PSE 476: Lecture 1813 Bleaching Sequences Nomenclature Rules (2) If washing is omitted, a parenthesis is added around the steps. »C(EO)D = Cl 2 /wash/NaOH/Oxygen/wash/ClO 2 /wash If chemicals are added simultaneously, the letters are placed in parenthesis separated by a + sign. C(E+O)D = Cl 2 /wash/NaOH+Oxygen/wash/ClO 2 /wash »People will also list this as CE/OD Sometimes small amounts of chemicals are added to fortify a step. The additives are typically listed as subscripts: E O or E P or E OP Subscripts are also used to designate differences in conditions (ie temp, pH, etc): D 0, D 1, D 2 If washing is omitted, a parenthesis is added around the steps. »C(EO)D = Cl 2 /wash/NaOH/Oxygen/wash/ClO 2 /wash If chemicals are added simultaneously, the letters are placed in parenthesis separated by a + sign. C(E+O)D = Cl 2 /wash/NaOH+Oxygen/wash/ClO 2 /wash »People will also list this as CE/OD Sometimes small amounts of chemicals are added to fortify a step. The additives are typically listed as subscripts: E O or E P or E OP Subscripts are also used to designate differences in conditions (ie temp, pH, etc): D 0, D 1, D 2

Pulping and Bleaching PSE 476: Lecture 1814 Differences in Chlorine Dioxide Stages ConditionD0D0 D1D1 D2D2 Final pH Temp °C40°C - 60°C55°C - 75°C60°C - 85°C Consistency10-15% Time30-80min2-4 hours Charge1-2 times kappa # 4-6 times kappa #

Pulping and Bleaching PSE 476: Lecture 1815 Bleaching Sequences Typical Bleaching Sequence (1990)

Pulping and Bleaching PSE 476: Lecture 1816 Bleaching Sequences Traditional Sequences

Pulping and Bleaching PSE 476: Lecture 1817 Bleaching Sequences Some Current (2001) Sequences