3rd Class Power Engineering (3B1) Practice Exam

The Kraft process, also known as the sulfate process, is a method used in the pulping of wood for papermaking. The primary chemical used in this process is sodium sulfate. This chemical plays a crucial role as it helps to break down the lignin that binds the cellulose fibers within the wood, allowing for the effective separation of the fibers necessary for paper production.

In the Kraft process, sodium sulfate is heated with wood chips in the presence of water, leading to a chemical reaction that results in the formation of sodium sulfide and sodium hydroxide. These reagents are essential for the subsequent cooking of wood chips, where the cellulose is extracted while significantly reducing the amount of lignin.

Sodium sulfate not only assists in the cooking process but is also recovered and reused, making the Kraft process more efficient and environmentally sustainable compared to other methods. This recovery aspect is important as it helps minimize waste and enhance the economic viability of the Kraft mill.

The other chemicals listed do not serve as primary reagents in the Kraft process: calcium hydroxide, potassium phosphate, and magnesium sulfate have different applications in various industrial processes but are not fundamental to the operation of the Kraft process. Thus, sodium sulfate is the key chemical that facilitates the efficient conversion of wood into