Abstract
Herein we studied the chemical structure of different types of lignin samples and the potential to prepare phenolic monomers was illustrated by phosphotungstic acid catalysts. Different types of H/G/S lignin components had different structures. The lignin extracted from poplar had the highest molecular weight and β‐O‐4 aryl ether contents, followed by pine and straw lignin samples. After depolymerization by PTA catalyst, the yields of phenolic monomers detected was 8.06 wt % (poplar), 5.44 wt % (pine) and 4.52 wt % (straw), respectively. Further, the ratios of H/G/S in the phenol monomers were also different, indicating that the S, G and H types structural units were continuously transformed with each other during the reaction. In our study, the change in the types of lignin samples resulted into an improvement of the distribution of phenolic products, and also the selectivity of phenolic monomers significantly.
Highlights
We consider that the structure of lignin is extremely different because of different types of lignin samples
Chemical analysis with the 2D-HSQC NMR revealed that types of lignin samples and solvent properties led to change in the lignin chemical linkage frequencies
The internal linkages within different types lignin samples are confirmed by 2D-HSQC NMR (Figure 1)
Summary
We studied the chemical structure of different types of lignin samples and the potential to prepare phenolic monomers was illustrated by phosphotungstic acid catalysts. Yang et al proposed a highefficient heterogeneous acid H-ZSM-5 catalysts depolymerization process with highly controllable products.[8] Besides, Deng et al reported that Keggin-type Cs + salts of polyoxometalates, showed firm acidity and catalyze the conversion of lignin to phenolic monomers.[9] Du et al studied that the use of phosphovanado molybdate for the cleavage of oxidative C C bonds.[10] Building on the above results, we discovered that polyoxometalate exhibits similar catalytic performance to those in a variety of reactions involving solid acids. The final goal was decided to the influence of the different types of lignin structure on the yield and distribution of phenolic monomers
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