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.
Secondary Peeling
Alkaline Depolymerisation
Thermal chemical reactions degrade carbohydrate chains stepwise following the random scission of internal glycosidic bonds in alkaline pulping liquors. Within high-temperature kraft digestions, secondary peeling cleaves monomer units from newly exposed reducing end groups along cellulose and hemicellulose backbones. The breakdown reduces pulp yield and degrades average fibre chain length throughout the chemical cook.
Reaction Kinetic
Cleavage reactions accelerate rapidly once cooking temperatures exceed one hundred and thirty degrees Celsius. At these elevated digester temperatures, hydroxide ions cleave intra-chain glycosidic links via alkaline hydrolysis, multiplying the number of active reducing end groups available for stepwise degradation. Each newly generated end group loses dozens of sugar monomers through consecutive beta-elimination reactions before a stopping reaction terminates the sequence.
Competing end-group conversion into stable metasaccharinic acid units eventually halts the stepwise depolymerisation along the carbohydrate polymer. Elevated alkali concentrations accelerate peeling rates, while lower cook temperatures favour chain survival and higher final brownstock yields. Pulp producers adjust cook profiles and chemical charges to balance delignification efficiency against carbohydrate preservation.
Chemical Stabilization
Chemical additives suppress stepwise depolymerisation by oxidising or reducing active end groups into stable configurations. Anthraquinone and polysulfide pre-treatments convert exposed aldehyde groups into carboxylic acids, preventing secondary peeling and preserving unbleached pulp yields.