Experimental Methodology for Heterogeneous Studies in Pulping of Wood

The heterogeneous nature of the kraft pulping of wood is experimentally demonstrated in this paper, and a new methodology for kraft pulping investigation is presented. The strategy proposed here enables the measurement of alkali and of lignin concentrations in the pulping liquor, both inside and outside of the wood chips. With this procedure, it is possible to independently determine, in both entrapped and free liquors, the time histories of the concentrations of alkali and lignin as well as total dissolved solids, which are a direct result of the mass transfer and of the chemical reactions that take place during this heterogeneous process. The influence of the chip thickness and of temperature on the relative rates of these two phenomena is also highlighted. This experimental methodology establishes the foundations for the development of a macroscopic heterogeneous kraft pulping model that can be experimentally validated in pulping conditions, even for modified digester processes.