Question

Cooking conditions in Kraft pulp process are

• A. Time 2-5 hrs, temperature 170-176$^\circ$C and pressure 660-925 kPa
• B. Time 6-12 hrs, temperature 125-160$^\circ$C and pressure 620-755 kPa
• C. Time 36-48 minutes, temperature 160-180$^\circ$C and pressure 660-1100 kPa
• D. Time 60-72 minutes, temperature 170-176$^\circ$C and pressure 660-1100 kPa

Hint:

The Kraft process requires a sustained cook ($2\text{--}5\text{ hours}$) at elevated conditions ($170\text{--}176^\circ\text{C}$) to properly delignify wood chips while preserving long fiber chains for high-strength paper.

Answer 1

The Correct Option is A

Concept: The Kraft process uses an alkaline cooking liquor (white liquor) to break down the lignin binding wood fibers together. This digestion occurs within large, high-pressure reactors called digesters, which can operate in batch or continuous configurations.

Step 1: Identifying standard industrial operating conditions.
To achieve complete chemical penetration and dissolve lignin without degrading the cellulose fibers, the digestion must be maintained within specific, controlled parameters:
• Cooking Temperature: Typically maintained between $170^\circ\text{C}$ and $176^\circ\text{C}$. Temperatures below this range drastically slow down the delignification rate, while higher temperatures can cause thermal degradation of the cellulose fibers, reducing pulp strength.
• Operating Pressure: Maintained between $660\text{ kPa}$ and $925\text{ kPa}$ ($95\text{--}135\text{ psi}$) to keep the liquor from boiling at these elevated cooking temperatures.
• Retention Cooking Time: Typically ranges from $2$ to $5\text{ hours}$, which includes the time spent ramping the reactor up to the target temperature. These standard industrial parameters match the values specified in option (1).