Kraft pulping diffusion

Increases in yield of naval stores are brought about by chemical treatment of the exposed wood, especially with paraquat herbicides (dipyridyl compounds). This treatment stimulates extensive oleoresin formation and diffusion into the wood, extending to the pith of the tree and several feet above the treatment level. As much as 40 percent oleoresin content in the wood has been produced. Such treatment could double naval stores production, for both gum and sulfate processes. It also has the potential of providing a new type of wood naval stores by solvent extraction prior to kraft pulping, or a combination of both methods. 

Studies carried out with the aim of developing models to estimate migration include a study by Aurela and Ketoja (2002). They estimated the diffusion rate of model compounds (butanol, ethanol, butyl acetate and tetrahydrofuran) in air at room temperature. They then measured the diffusion of these substances through papers with different grammages (and hence, porosities) produced from birch Kraft pulp. The model compounds were not in contact with the test papers and hence transferred via the gas phase. They concluded that the diffusion constants determined in air could be used in random walk simulation to predict migration in a fibre network. Random walk simulations are a mathematical means of modelling processes based on probability distribution and are often applied to investigate diffusion processes. 

A Wojciak, M Sikorski, R Gonzalez Moreno, JL Bourdelande, and F Wilkinson. The Use of Diffuse-Reflectance Laser-Flash Photoysis to Study the Photochemistry of the Kraft Pulp Treated with Hydrogen Peroxide under Alkaline and Acidic Conditions. WoodSci. Technol. 36 187-195, 2002. 

CJ Jacobs-Young, RR Gustafson, JA Heitmaim. Conventional kraft pulping using enzyme pretreatment technology Role of diffusivity in enhancing pulp uniformity. Paperi Ja Puu-Paper and Timber 82(2) 114—119, 2000. 

An electrochemical reactor with anolyte and catholyte divided by a cation-permeable membrane or semipermeable separator is required to preclude the diffusion of sulfide/polysulfide anions from anolyte to catholyte and to avoid reduction of polysulfide formed at the anode by reaction (9), being reduced at the cathode by the reverse reaction. Similar processes have been reported [18] for producing polysulfide (and hydroxide) solutions at current densities of 5 kA m for Kraft paper pulping processes. 

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