Separation of dihydrosinapyl alcohol from reductive depolymerization products of lignin by multistage extraction and crystallization

Because of the high complexity of the product and the similar physicochemical properties between G and S counterparts, the separation of aromatic monomers is one of the greatest challenges in the lignin chemical valorization, which limits its further utilization and conversion. In this study, the preparation method of the dihydroconiferyl alcohol & dihydrosinapyl alcohol-enriched oil and high purity dihydrosinapyl alcohol from reductive catalytic fractionation products catalyzed by Pd/C was first reported. Moreover, a purification process with alkali extraction - organic solvent extraction - dichloromethane reverse extraction - crystallization in the KOH ethanol solution as the main unit operation was designed. As a result, a monomer-enriched oil in which dihydroconiferyl alcohol (G-3OH) and dihydrosinapyl alcohol (S-3OH) could totally account for more than 83% was obtained, and S-3OH with a purity of 90.2% was separated by crystallization. In addition, this purification process was scaled up to 10 times. The monomer-enriched oil with a G-3OH and S-3OH content of 87.2% was obtained. The recoveries of G-3OH and S-3OH were 81.0% and 91.5%, respectively. The purity of S-3OH was 89.4%, and the recovery was 51.6%. The integrated process realizes the effective separation of the reductive depolymerization products of lignin, which can provide technical support for its industrial production.