What happens during the second step of the Kraft process after wood chips are cooked?

In the Kraft process, which is utilized for producing pulp from wood chips, the second step involves managing the pulp after cooking. When wood chips are subjected to cooking with sodium hydroxide and sodium sulfide, they undergo a chemical transformation that breaks down lignin, allowing the cellulose fibers to remain intact.

After cooking, the pulp is typically washed to remove the cooking chemicals, resulting in a mixture that includes both pulp and weak black liquor, which contains dissolved lignin, hemicellulose, and other components removed during cooking. This step is crucial for ensuring that the pulp can be further processed without the interference of these unwanted substances.

Separating the pulp from weak black liquor is essential as it allows for the recovery of these valuable chemicals, which can be reused in the process. Consequently, this separation is a key operation that establishes the foundation for subsequent steps, such as bleaching and drying, which occur later in the process. Therefore, the identification of the separation of the pulp from weak black liquor as the second step accurately reflects what occurs after the cooking phase in the Kraft process.