Revisiting the Question of Birch Wood Delignification in the Potassium Hydroxide–Hydrazine–Isobutyl Alcohol–Water System

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Abstract

In this investigation, potassium hydroxide is used as the main delignification reagent and as a base for the creation of a composite cooking system that also consists of hydrazine, isobutyl alcohol and water. The ultimate purpose is to further develop the technology of alkaline pulping in order to produce cellulose. The aim of this research is to establish what effect this system has on the delignification of birch wood and also to discover what role hydrazine plays in the process. The special features of delignification in this system are the preliminary impregnation of the wood chips with an aqueous solution that contains potassium hydroxide and hydrazine, the collection of the excess solution used for impregnation, and the subsequent introduction of isobutyl alcohol in the cooking process. The variable factors in this investigation were the concentration of potassium hydroxide in the impregnating solution (from 80 g K₂O/dm³ to 200 g K₂O/dm³) and the final cooking temperature (from 120 °C to 140 °C). As a result of the experiments, cellulose was obtained with a wide range of pulp yields, from 46.6 % to 55.2 %, and a lignin content of from 2.4 % to 17.6 % by weight of pulp. When the final temperature was reduced from 140 °C to 130 °C (with no change in the cooking time), delignification of the birch wood down to the same content of residual lignin was accompanied by a significant increase in the concentration of potassium hydroxide in the impregnating solution. At a temperature of 125 °C or less, delignification slowed down substantially, so much so that, within the range of potassium hydroxide concentrations used in the impregnating solution, it was impossible to obtain cellulose with a lignin content of less than 5.6 % by weight of wood. It was discovered that, when it is used as a reducing agent, hydrazine exhibits the greatest activity during decomposition into the gaseous components N₂, H₂ and NH₃. The higher the cooking temperature, the greater the consumption of hydrazine in chemical reactions and the deeper the process of delignification in birch wood, given that the cooking time remains the same, as does the concentration of potassium hydroxide in the impregnating solution. When the final cooking temperature is reduced to 125 °C, the delignification process is sharply retarded (and even more so if it is reduced to 120 °C), even if the concentration of potassium hydroxide is increased up to 200 g K₂O/dm³, and the degradation of carbohydrates is intensified. In the end, it was established that the final cooking temperature of birch wood in a potassium hydroxide – hydrazine – isobutyl alcohol – water system is limited by the temperature at which hydrazine begins to decompose into the gaseous products, and this temperature can be reduced to 130 °C without any detriment to the pulp yield and the rate of delignification.

Authors

• V.A. Udal'tsov, Postgraduate Student
• G.A. Pazukhina, Doctor of Engineering, Professor
  
  
  St. Petersburg State Forest Technical University,
  Institutskiy per., 5, St. Petersburg, 194021, Russia;
  е-mail: vudalcv@rambler.ru,
  е-mail: gal.pazukhina@yandex.ru

Affiliation

Keywords

References

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