Pulp and paper — sulfate (kraft) pulping conditions In the sulphate (kraft) process, the cooking conditions in the digester are typically closest to which pressure–temperature combination?

Introduction / Context:
Kraft pulping (sulphate process) digests wood chips in white liquor (NaOH and Na2S) to remove lignin and liberate cellulose fibers. The process requires elevated temperature and pressure to accelerate delignification without degrading cellulose excessively.

Given Data / Assumptions:

• Typical batch or continuous digesters operate well above the boiling point of water.
• Temperatures are usually around 160–180°C; pressure corresponds to saturated steam at those temperatures plus liquor vapor pressure.

Concept / Approach:
At 170–180°C, saturated steam pressures are several atmospheres. Industry operations commonly cite roughly 7–12 atm (absolute) during the cook, consistent with option (b).

Step-by-Step Solution:
Eliminate unrealistic extremes: 800°C is far beyond chemical pulping conditions.Near-atmospheric pressure cannot maintain water at 170–180°C.Thus, 10 atm and 170–180°C matches realistic kraft pulping conditions.

Verification / Alternative check:
Process descriptions confirm cooking at approximately 170°C with corresponding saturated pressures, ensuring effective delignification.

Why Other Options Are Wrong:

• 800°C: thermal destruction; not a liquid-phase cook.
• 1 atm at 170–180°C: impossible for aqueous systems without pressure.
• 1 atm at 800°C: physically irrelevant for this process.

Common Pitfalls:

• Confusing kraft cook with high-temperature pyrolysis or gasification.

Final Answer:
10 atm, 170–180°C