Chromatographic separation of wood constituents
Hot water extracted Norway spruce was fractionated by cross flow filtration followed by two stages of hydrophobic adsorption with increasing hydrophobic selectivity. Three fractions were recovered and characterized by Klason and sugar content and by size exclusion measurements of enzymatically hydrolyzed samples, revealing species covalently bound to carbohydrates. The fractions were mainly characterized by contents of aromatic species, where the first fraction contained about 56 % lignin, the second contained about 10 % lignin and the third about 1.5 % lignin. The non-lignin part of the fractions consisted of hemicelluloses, mainly galactoglucomannan. The method investigated proved successful in separating lignin, LCCs and carbohydrates with mild processing which does not affect the molecular structure of the species.
A mathematical model describing the migration of wood model constituents in a chromatographic column has been developed. A combination of the frontal analysis (FA) method and pulse injection break through measurements were used to estimate the parameters describing solute migration for a simplified model system. The parameters estimated concerned the mass transport phenomena of axial dispersion, film mass transfer and particle diffusion. The hydrophobic affinity parameters were also determined in form of isotherms and the effect of mobile phase modifier. Also; the packed bed parameters of bed porosity and particle porosity were determined. The model accuracy was verified to be within 95 %.
The particle pore size is suspected of limiting the capacity of the sorbent. Also, the relatively small particle sizes used induces quite high pressure drop over the column which must be optimized in a large scale process.