News Excerpt:

The Kraft process is ubiquitous today and replaced more toxic and resource-intensive methods to produce paper.

About Kraft Process:

• It is a technique that accepts wood chips as input to produce cellulose fibers, which are then used to make paper and other materials used in everyday objects.
• The process is chemical in nature -
  • The chips are treated with water, sodium hydroxide, and sodium sulphide – the last two solutions form a highly alkaline mixture called white liquor – at a relatively high temperature. 
  • This breaks the bonds between lignin (an organic polymer and important constituent of cell walls), hemicellulose (cellulose-like fibers that are shorter), and cellulose. 
  • The step is followed by those to obtain the wood pulp, wash off, and recover the reaction chemicals, bleaching, and processing.
• The strength of the paper produced by a chemical process like this is determined by its sulphidity, i.e. the relative amount of sulphur it contains.
  • Kraft-process paper has higher sulphidity than that produced by other processes.

Challenges with Kraft Process:

• Resource Demand: It requires a large volume of water.
• Unfriendly with environment: The process of removing lignin from the wood chips discharges the lignin through water along with dissolved carbon, alcohol ions, and heavy metals.
• While these substances can be removed from the effluent before it dissolves in a water body, the fact that they’re produced at all makes the kraft process environmentally unfriendly.

Way Forward: For improving overall operating performance at existing kraft pulp mills is through advanced energy integration and mill-wide control. Although limited automatic control of the individual units that make up the process is available, there is presently no effective control strategy overseeing the entire cycle which needs to be addressed.