Today, the production of tall oil in pulp mills is primarily conditioned by chemical products and wood quality required for the manufacturing process.
The main chemical component to produce tall oil is sulfuric acid, requiring about 200 - 300 kg/ton of crude tall oil, depending on the quality of the soap, which raises the cost of the process.
On the other hand, the type of wood has an effect on the quality of tall oil because different woods produce different types of resin acids, fatty acids and unsaponifiables, and thus different amounts of tall oil. In general, older and slowest-growing trees produce more resin acids.
The process to produce tall oil uses tall oil soap obtained specifically from black liquor resulting from the pulping process, which reacts with sulfuric acid to certain time and temperature conditions. This reaction favors the reduction of the pH from the solution that is close to 12 to a value below 8. At this pH level, the acidified crude tall oil is separated into two streams by a centrifugation process: crude tall oil (lighter phase) and brine (mainly sodium sulfate and lignin containing hydrogen sulfide).
For the reasons mentioned above, the kraft pulp industry requires new processes to produce tall oil that would allow reducing the costs associated with the consumption of chemical substances and obtaining a high quality tall oil.
Due to the growing increase in the cost of sulfuric acid and soda, Planta Arauco decided to request the Technological Development Unit (UDT) of the Universidad de Concepción, the technical, economic and environmental evaluation of replacing sulfuric acid used in Tall Oil Plant by the acid salt of sodium sesquisulfate produced in the chlorine dioxide plant.