文档介绍：New Technologies
In Pulp Bleaching
Introduction
Oxygen Delignification
Ozone Delignification
Peroxide Bleaching
Peracid Bleaching
Hydrosulfite Bleaching
Chlorination
Chlorine Dioxide Bleaching
Enzyme Treatment of Pulp(Biobleaching)
INTRODUCTION
Objectives
●Brightness ●Cleanliness
●Purification-dissolving grade
Historical background
Major concerns
◇Costs ◇Environmental ◇Energy
Chemical
Function
Pulp
Advantage
Disadvantages
Cl2
Oxidize and chlorinate
C
Effective, economical delignification; good particle removal
Organochlorine formation; highly corrosive
NaOCl
Ca(Ocl)2
Oxidize, decolorize, and solubilize lignin
C
Easy to make and use; low cost
Can cause loss of pulp strength; chloroform formation
ClO2
1)Oxide, decolorize and solubilize lignin
2) In small amounts with Cl2; protects against cellulose degradation
C
Achieve high brightness without loss of pulp strength; good particle bleaching
Must be made on-site; cost; anochlorine formation; highly corrosive
Functions, advantages and disadvantages of bleaching chemicals
Chemical
Function
Pulp
Advantages
disadvantages
O2
Oxidize and solubilize lignin
C
Low chemical cost; provides chlorine-free effluent for recovery
Requires significant capital equipment when used in large amounts; potential loss of pulp strength
H2O2
Oxidize and decolorize lignin
C or M
Easy to use; Low capital cost
High chemical cost; Poor particle bleaching; Can cause loss of pulp strength
O3
Oxidize, decolorize and solubilize lignin
C
Effective, provides chlorine-free effluent for recovery
Must be made on-site; cost; poor particle bleaching and pulp strength
Functions, advantages and disadvantages of bleaching chemicals
Chemical
Function
Pulp
Advantages
disadvantages
Na2S2O4
Reduce and decolorize lignin in high-yield pulps
M
Easy to use;
Low capital cost
poses readily; Limited brightness gain
Xylanase
Catalyze xylan hydrolysis and aid in lignin removal
C
Easy to use; Low capital cost
Limi