The straw ammonium sulfite pulp is completely free from chlorine-based bleaching agents

（NH4）2SO3+2NaOH→Na2SO3+2NH3+2H2O

When ammonium hydroxide reacts with strong acids, it releases sulfur dioxide:

（NH4）2SO3+H2SO4→（NH4）2SO4+SO2+H2O

1.2.2 Mechanism of subammonium pulping

The ammonium subnitrate pulping process is designed to avoid the hydrolysis of cellulose and hemicellulose in acidic solutions, prevent the delignification reaction occurring in alkaline solutions, and utilize alkaline hydrolysis to enhance the pulp yield. During the cooking process, the sulfonation and dissolution mechanisms of lignin are consistent with those observed in the acid sulfate pulping method. The primary chemical reaction in delignification is the sulfonation of lignin, wherein lignin reacts with the ammonium subnitrate solution to form lignin sulfonates. Sulfonic acids—organic acids containing a sulfonic group—are generally soluble in water; consequently, the resulting lignin sulfonates and their salts are dissolved out of the system. As a result, the cooking liquor remains within a neutral pH range. This slower rate of lignin sulfonation and dissolution necessitates a longer cooking duration compared to the sulfate pulping method. To neutralize the deacetylation reactions of hemicellulose during the cooking process, as well as the organic acids generated by the decomposition of cellulose and hemicellulose under high-temperature conditions, ammonia water, urea, or similar agents are added as buffer agents in the ammonium subnitrate pulping process. This ensures that the final pH value of the cooking effluent exceeds 7, thereby reducing corrosion of the equipment and improving the pulp yield.