Abstract

More than 900 papers related to organosolv pulping have been reviewed in this thesis. From the information included in those papers it can be concluded that organosolv pulping processes are still in a developing stage and are not yet ready to seriously threat the position of the kraft process as the main pulp manufacturing process in the world.

Distillation seems to be the main alternative as the process for recovering the solvent in organosolv pulping. A good reason for this is that using simple distillation no potentially harmful components are introduced to the process.

The effect of feed composition on the operation of a separation sequence in an organosolv process using aqueous formic and acetic acids and corresponding peroxyacids was studied. When simple distillation was used as the separation method the effect was found to be significant. The no ideal nature of the formic acid-acetic acid-water mixture, which separation was studied, makes the ternary composition space to divide into four distillation regions. Which region the feed is located in, obviously determines the economy of the distillation sequence.

Shortcut calculation methods cannot be recommended to be used for designing a distillation sequence for the ternary mixture studied, but they give useful information for the comparison of such sequences. They were used to choose a limited number of alternatives for studies with rigorous calculation methods.

Minimum work of separation can also be used to make a satisfying estimate for the relative easiness of separation of the formic acid-acetic acid-water mixture.

Thermal integration using pinch technology was also tested and found very useful for decreasing the thermal energy consumption of distillation processes.

Thermodynamic efficiencies for separating the formic acid-acetic acid-water mixture by simple distillation were estimated. They were found to be lower than the average value for distillation presented in literature.