2 research outputs found
Physicochemical Modeling for Hot Water Extraction of Birch Wood
This
paper presents a model developed for hot water extraction of birch
wood meal. Besides solids, two liquid phases are assumed in the system:
liquid bound to a wood fiber wall and the other remaining external
liquid. True chemical species, their reactions, and diffusion between
the liquid phases are considered in the model. The breakdown of hemicellulose
into short-chain polymers and monomeric sugar units is modeled by
applying an accurate and computationally efficient population balance
approach. State-of-the-art correlations and equations are used, thus
aiming for a truly predictive model. Several thermodynamic and kinetic
submodels are integrated to achieve additional information compared
to models already presented in the literature. The presented model
is capable of reproducing the measured concentration profiles of chemical
species and molecular weight distribution of hemicellulose polymers
as a function of the process conditions. The output concentration
data are further utilized to calculate the dissolved species and pH
in the two liquid phases. Eventually, it could be utilized in optimizing
a batch hot water extraction process to maximize either the yield
of long-chain hemicelluloses or their monomeric sugars
Novel Insight into Lignin Degradation during Kraft Cooking
In
this study three different modeling approaches, with varying
levels of sophistication and complexity, on modeling kraft cooking
kinetics have been investigated. In the first and second approaches,
isothermal conditions were used by converting the heating and cooling
times into isothermal time. In the third approach, real temperature
and time were used. Donnan theory, accounting for the cation exchange
property of the wood fibers, was used in the second and third approaches
for estimation of the cooking chemical concentrations in the fiber
wall liquid, whereas in the first approach the cooking chemical concentrations
in the bulk liquid phase were used. A modification of the Purdue model
was used for modeling the delignification kinetics. The parameters
of the Purdue model were regressed both with Matlab (commercial software)
and Kinfit (in-house software). All three regressions with different
modeling approaches provided very good fits to the experimental data.
When Donnan theory and real temperature profiles (third approach)
were employed, the estimated reaction rates for the faster reacting
lignin subcomponent in the Purdue model decreased at all temperatures.
On the other hand, the portion of the faster reacting component increased
from 24% to 28%. In this way the third modeling approach mimics the
reality in the most accurate way. Its implementation is more tedious,
but the model should have more predictive capabilities. Furthermore,
the effect of anthraquinone on kraft cooking kinetics was studied