Delignification

PULP AND PAPER PROCESSES: PRAXAIR'S OXYGEN DELIGNIFICATION & EXTRACTIVE OXIDATION

Oxygen Delignification

Delignification is the act of processing the chemical structure of lignin so that it can be dissolved in the paper production process. With chlorine gradually being phased out of the bleaching process, and oxygen being the least expensive bleaching chemical in the mill, oxygen delignification offers significant operating cost advantages over delignification processes which use bleaching agents such as chlorine dioxide and hydrogen peroxide.

Savings earlier in the production process

delignification process diagramOxygen delignification offers significant operating cost advantages and is a recognized way to enhance yield in bleached pulp production. An important environmental impact of oxygen delignification is the reduction or elimination of adsordable organic halides (AOX). Other benefits include lower biochemical/chemical oxygen demand.  Praxair provides technical support for the oxygen delignification application and will work with you to help select the appropriate system for your mill’s unique operating situation. 

There are two types of oxygen delignification: High Consistency Oxygen Delignification (HCOD) and Medium Consistency Oxygen Delignification (MCOD).  

Oxygen Delignification (131KB)

Selecting the appropriate type of delignification system involves careful consideration of each mill's unique operating situation and the balance between installation and operating costs.

Benefits:

  • After initial cost, lower overall bleaching chemical requirements
  • AOX is reduced or eliminated
  • Lower biological oxygen demand/chemical oxygen demand and less color in the effluent
  • Better yield than extended cooking
  • An important step towards total chlorine free or elemental free pulp production and mill closure

Reinforcing Extraction with Oxygen and Peroxide

Because the process conditions during the extraction stage are optimal for the addition of oxygen and hydrogen peroxide, Praxair also offers oxygen- and oxygen-and-peroxide-reinforced extraction as an application related to delignification. Adding these components during the alkaline extraction stage reduces the chemical demand of chlorine dioxide in subsequent stages. While the addition of hydrogen peroxide improves product brightness, the addition of oxygen selectively reduces the lignin content of the pulp. Both types of extraction are applicable to all bleaching sequences.