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Abstract
A method is developed to assess the limits of selective depolymerization, that is, splitting of aryl ether bonds to yield monomeric aromatic products, of native and technical lignins. The method and respective formula is based on measuring the difference between a sum of aryl ether bonds (α-О-4 and β-О-4) and sum of 5-5 and 4-O-5 bonds. The values calculated based on the proposed formula are correlated with published experimental data on catalytic degradation of lignin. In all cases, wood species and experimental conditions notwithstanding, the yields of monomeric aromatic products are found to be close to theoretically calculated for both softwood (23%) and hardwood (51%). Notice that in the actual experiments the yield in hardwood is twice as much as in softwood. In technical lignins (kraft, organosolv) the yields of monomeric products are lowed due to splitting of α-О-4 and β-О-4 bonds during pulping. The developed method is helpful in evaluation of technologies aiming to bring value-added products from lignin through selective degradation.
