华南理工大学：《制浆原理与工程》9New Technologies In Pulp Bleaching

New Technologies In Pulp bleaching South China University of Technology

South China University of Technology New Technologies In Pulp Bleaching

Introduction oXYgen Delignification Ozone delignification a Peroxide Bleaching Peracid Bleaching a Hydrosulfite Bleaching ■Ch| urination a Chlorine Dioxide Bleaching a Enzyme Treatment of Pulp(Biobleaching) South China University of Technology

South China University of Technology Introduction Oxygen Delignification Ozone Delignification Peroxide Bleaching Peracid Bleaching Hydrosulfite Bleaching Chlorination Chlorine Dioxide Bleaching Enzyme Treatment of Pulp(Biobleaching)

INTRODUCTION ■ Objectives ● Brightness ○c| earliness O Purification-dissolving grade a Historical background ■ Major concerns ◇ Costs◇ Environmental◇ Energy South China University of Technology

South China University of Technology INTRODUCTION Objectives ●Brightness ●Cleanliness ●Purification-dissolving grade Historical background Major concerns ◇Costs ◇Environmental ◇Energy

Functions, advantages and disadvantages of bleaching chemicals Chemical Function Pulp Advantag Disadvantages e Cl2 Oxidize andC Effective Organochlorine chlorinate economical delignification formation good particle removal highly corrosive Naocl Oxidize c Easy to make Can cause loss of decolorize. and and use: low pulp strength Ca(Ocl)2 solubilize lignin cost chloroform formation CIO 1)Oxide, c Achieve high Must be made on decolorize and brightness solubilize lignin without loss of site: cost: some 2)In small pulp strength;I organochlorine amounts with cI2 good particle formation; highly protects against bleaching corrosive cellulose degradation

Chemical Function Pulp Advantag e 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; some organochlorine formation; highly corrosive Functions, advantages and disadvantages of bleaching chemicals

Functions, advantages and disadvantages of bleaching chemicals Chemical Function Pul Advantage disadvantag p es Oxidize and Low chemical Requires significant solubilize lignin cost; provides capital equipment chlorine-free when used in large effluent for amounts potential recovery loss of pulp strength H2O2 Oxidize and C or Easy to use; High chemical decolorⅰze M Low capital cost: Poor lignin cost particle bleaching Can cause loss of pulp strength O3 Oxidize Effective Must be made decolorize and provides on-site: cost: poor solubilize lignin chlorine-free particle bleaching effluent for and pulp strength recovery

Chemical Function Pul p Advantage s disadvantag es 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

Functions, advantages and disadvantages of bleaching chemicals Chemica Function Pul Advantage disadvantag pS es Na2S20 Reduce and MEasy to use;Decomposes decolorize ow capital readily Limited lignin in high cost brightness gain yield pulps Xylans Catalyze xylan c Easy to use; Limited hydrolysis and ow capital effectiveness aid in lignin cost COS removal NaOH Hydrolyze C Effective Darkens pulp chlorolignin and solubilize Economic lignin al EDTA Removal Improves Cost peroxide DTPA meta selectivity and

Chemica l Function Pul p Advantage s disadvantag es Na2S2O 4 Reduce and decolorize lignin in high￾yield pulps M Easy to use; Low capital cost Decomposes readily; Limited brightness gain Xylanas e Catalyze xylan hydrolysis and aid in lignin removal C Easy to use; Low capital cost Limited effectiveness; cost NaOH Hydrolyze chlorolignin and solubilize lignin C Effective Economic al Darkens pulp EDTA DTPA Removal metal ions C Improves peroxide selectivity and efficiency Cost Functions, advantages and disadvantages of bleaching chemicals

Reactions of different oxidants used in bleaching Cl2+2e→2C Naocl+h o+2e-NaCl+20H- Clo,+2H.0+5e CI-+40H- O2+2H2O+4e-40H H2O2+2H+2e→2H2O 0,+3H++6e-30H- South China University of Technology

South China University of Technology Reactions of different oxidants used in bleaching Cl2+2e-→2Cl￾NaOCl+H2O+2e-→NaCl+2OH￾ClO2+2H2O+5e-→Cl-+4OH￾O2+2H2O+4e-→4OH￾H2O2+2H++2e-→2H2O O3+3H++6e-→3OH-

■B| eaching sequence TWo improtant aspects of establishing the proper sequence of bleaching:★cost★ Selectivity I Typical bleaching sequences ●CEH●(C+ D)EODED ODEODED● OZEOD ●oQP YP Coventional sequences for KP CEDED CEHDED Softwood CEDED CEHD Hardwood South China University of Technology

South China University of Technology Bleaching sequence Two improtant aspects of establishing the proper sequence of bleaching: ★Cost ★Selectivity Typical bleaching sequences ●CEH ●(C+D)EoDED ●DEoDED ●OZEoD ●OQP ●YP Coventional sequences for KP CEDED CEHDED Softwood CEDED CEHD Hardwood

■ New sequences OCEODED CDEODE D OCDEOD OZED XEODDED New development ECF--OPDED ODEDD TCF-OZEP OQPZP OQPP South China University of Technology

South China University of Technology New sequences OCEoDED CDEoDEpD OCDEoD OZED XEOPDED New development ECF—OPDED ODEDD TCF—OZEP OQPZP OQPP

Typical process conditions for bleaching softwood KP chemical Naoh CIO laOh CiO2 Water Water Steam Water Steam Steam Unbleached pulp D Eo D LBI leached pulp Effluent to Acidic Alkaline effluent recovery effluent South China University of Technology

South China University of Technology Unbleached pulp Effluent to recovery NaOH O2 Water & Steam Acidic effluent ClO2 Water NaOH O2 Water & Steam Alkaline effluent Water & Steam O2 ClO2 Bleached pulp O D Eo D Typical process conditions for bleaching softwood KP chemical