Alkaline Hydrolysis Kinetics and Carbohydrate Retention in Continuous Digesters
Controlling effective alkali profiles and temperature in continuous digesters maximizes xylan retention, stabilizing pulp yield and securing compliance files.
Glucomannan Loss
Carbohydrate Degradation
Degradation of the primary hemicellulose in softwood species occurs during the initial stages of alkaline pulping. This chemical breakdown, termed glucomannan loss, reduces the total pulp yield and affects the refining behavior of the fibers. Softwoods contain high concentrations of glucomannan, making its preservation a priority for mills trying to maximize fiber output.
When this polymer degrades, the resulting pulp produces paper with lower tensile strength and bonding potential, which directly impacts the performance of paperboard used in packaging.
Chemical Mechanism
Reaction of the polymer chain with sodium hydroxide initiates the alkaline peeling process from the reducing end. This chemical pathway is the primary driver of glucomannan loss in kraft pulping, especially before the temperature reaches one hundred and twenty degrees Celsius. The individual glucose and mannose units are sequentially cleaved until a termination reaction stops the process.
Some polymers are also lost through direct dissolution in the highly alkaline cooking liquor.
Process Control
Minimizing the loss of these hemicelluloses requires careful control of the initial alkali concentration in the digester. Additives such as anthraquinone can suppress the glucomannan loss by oxidizing the reducing groups to stable acids. This protection improves the yield of the kraft pulp process.