Atmospheric pulping

Project description

Chemical pulping is generally performed by incubation of wood or other plant biomass with alkaline or alkalic solutions, and in most cases, in the presence of active sulfur-containing chemicals, at high temperatures for some hours. Due to the temperature being higher than the boiling point of water, overpressure is needed for the process which makes investment costs for equipment very high. On the other hand, the costs for process chemicals can be manageable since process chemicals could be made from the consumed process liquids such as black liquor from the kraft process so that valuable byproducts could be obtained from the consumed process, that purchase of pulping chemical may be possible, i.e., brown liquor from sulfite pulping. One interesting possibility could be modifying the pulping conditions/chemistry to obtain more valuable lignin. Presently, there is a large interest in performing pulping in organic solvents rather than in water due to that the lignin obtained has interesting properties such as being more hydrophobic. However, a common problem with frequently used organic solvents such as methanol and ethanol is that they have a lower boiling point than water, which means overpressure during pulping conditions is even higher than traditional water-based pulping. As a consequence, even higher investment costs are needed which have severely hampered its commercialization. 

Another concept is also investigated where the pulping liquor, glycerol, has a higher boiling point which means that the pulping is actually performed under the boiling point of glycerol and can therefore be done at atmospheric pressure, i.e., in an open container. In preliminary studies, we have demonstrated that a glycerol version of kraft pulping can be performed on softwood with good results. Although the equipment may probably be much simpler for this process than for traditional pulping, chemical regeneration is a more intricate problem and novel glycerol must probably be purchased for every pulping cycle, which is a problem even though glycerol is a rather cheap component. However, the black liquor lignin obtained from this process will most likely have interesting properties. The remaining black liquor can probably be used for the electrochemical generation of hydrogen and the residual can be burned for the production of NaSH and NaOH.

Since this type of pulping equipment will probably be much cheaper than conventional chemical pulping, the method might be especially interesting for relatively small-scale applications, such as pulping of byproducts from the food industry.

Financing

Knut and Alice Wallenberg foundation

Collaborators

Gunnar Henriksson, KTH

Olena Sevastyanova, KTH

Martin Lawoko, KTH