[PDF] Réduction de limpact environnemental du blanchiment au peroxyde

View - Download Réduction de limpact environnemental du blanchiment au peroxyde

Previous PDF

Next PDF

A b aa a bbab b a b a a b bb b b b aa bb b a bbbb Al Al Al b Al a a Al Al Al tl tl Al tl tl t t t t t t t t t t t l a a b A l ab aaaaa ab a a Al Al b b Al a Al a b b b Al Al Al A A A f AA a l A A f baa u l ln FF t l lndn e e 253,7 dn

ABSTRACT

In the pulp and paper industry, environmental and safety regulations have become the driving force behind the development of technologies that minimize the genera- tion of waste into the environment. We reported new alkalis tested to replace NaOH in H 2 O 2 bleaching of ther- momechanical pulp (TMP), since the strong alkalinity of sodium hydroxide solubilizes wood substances and results in a high chemical oxygen demand (COD) load. The aim of this work was to reduce COD values, parti- cularly recalcitrant COD (R-COD), without losing pulp brightness. Studies have recommended replacing NaOH with other compounds such as Mg(OH) 2 , MgCO 3 and

Ca(OH)

2 . Although the experiments globally reflected the impossibility of totally substituting NaOH, NaOH/

Mg(OH)

2 and NaOH/MgCO 3 mixtures gave the same brightness with a significant decrease in COD. The bright- ness target was reached with low recalcitrant COD when

NaOH/silicate/Mg(OH)

2 and NaOH/silicate/MgCO 3 mix- tures were 1 %/0.75 %/0.75 %. Compared to conventio- nal bleaching, COD was about 26 % and 31 % lower for

Mg(OH)

2 - and MgCO 3 -based bleaching, respectively, consequently generating 10 and 8 kg O 2 ton -1 of R-COD whereas conventional bleaching produced 13.3 kg O 2 ton -1 . These promising alternatives were successfully vali- dated at semi-industrial scale.

KEYWORDS

Brightness; bleaching; BOD; COD; hydrogen peroxide; magnesium carbonate; magnesium hydroxide; recalci- trant COD; sodium hydroxide; thermomechanical pulp (TMP).

INTRODUCTION

Peroxide bleaching is the dominant process in thermo- mechanical pulp bleaching as it is the most efficient tech- nology for reaching high levels of brightness. Conventio- nal peroxide bleaching uses NaOH as alkali source, yet its strong alkalinity can cause major dissolution of lignin and hemicelluloses, which increases effluent pollution load and decreases pulp yield (Holmbom et al.1991; and impending legislation (Harrigan 2008) are liable to substantially increase the cost availability of sodium hydroxide, making it of interest to investigate alternative sources of alkali. Recent studies have shown that replacing NaOH with

Mg(OH)

2 , Ca(OH) 2 and MgCO 3 in peroxide bleaching of thermomechanical pulp could offer many benefits, lower effluent COD load and higher effluent bleaching yield (Depew et al.1999; Dietz et al.2008; He et al.2006;

2008; Suess

et al.2001), as well as decreased oxalate- related scaling in the bleach plant (Yu et al.2004). Suess et al.(2001) reported that magnesium hydroxide was a very attractive alternative alkali source for bleaching mechanical pulps, offering a 30-40 % decrease in COD plus significant decreases in sodium silicate charge resul- ting in less anionic trash formation. Depew et al.(1999) observed that alkali-free mechanical pulp bleaching using magnesium carbonate was able to reduce biological oxy- gen demand (BOD) due to the neutral pH of the treat- ment, while brightness values remained at least as good as conventional alkali peroxide bleaching processes. More recently, Sewing (2008) concluded that using cal-

Vol. 65 - n°1 >> Février-Mars 2011

BLANCHIMENT DESPÂTES

14

Reducing environmental impact

by using weak alkalis in mechanical pulp bleaching

Savoye L., Meyer V., Petit-Conil M.

Centre Technique du Papier (CTP) - InTechFibres, Domaine Universitaire, BP 251, 38044

Grenoble Cedex 9, FRANCE

Corresponding author: liliane.savoye@webctp.com

Vol. 65 - n°1 >> Février-Mars 2011

15

BLANCHIMENT DESPÂTES

cium hydroxide instead of sodium hydroxide in peroxide bleaching of groundwood pulp was a feasible alternative, as it gave considerable improvements in wastewater load and fibre loss while saving on chemical costs. Biodegradability data on the organic compounds released in bleaching effluents is scarce. This study therefore aimed to optimize the alkaline peroxide bleaching condi- tions of thermomechanical pulp to reduce the recalcitrant COD of the corresponding effluents so as to limit the dis- charge of components and waste into water and soil. For this purpose, we evaluated new alkali sources such as

Mg(OH)

2 , MgCO 3 and Ca(OH) 2

MATERIALS

quotesdbs_dbs27.pdfusesText_33

[PDF] Blanchiment et congélation - Fruits Et Légumes

[PDF] blanchir - Le Menu - Support Technique

[PDF] Blanchir le linge sans eau de javel - Anciens Et Réunions

[PDF] BLANCHISSERIE

[PDF] Blanchisserie de Waterloo Tarif de blanchisserie

[PDF] Blanchisserie industrielle - France

[PDF] Blanchisserie professionnelle - Anciens Et Réunions

[PDF] Blanchisserie Vêtements de travail : location, vente, entretien - Anciens Et Réunions

[PDF] Blanchot et la question du centre de l`oeuvre - Pierre Pachet

[PDF] BLANCKAERT Gilbert - Anciens Et Réunions

[PDF] Blanco

[PDF] BLANCO ALTA-F Compact BLANCO ALTA-S

[PDF] BLANCO ALTA-S Compact Vario

[PDF] Blanco Außenseite..

[PDF] BLANCO AXIS II 6 S-IF Edition pour four vapeur