Catalytic depolymerization of Kraft lignin to high yield alkylated-phenols over CoMo/SBA-15 catalyst in supercritical ethanol

Lignin is generally considered to be a renewable and sustainable resource of aromatic chemicals. However, the depolymerization of Kraft lignin (KL) for the production of selective phenolic monomers presents a significant challenge due to its highly recalcitrant nature. Therefore, in this work, we investigated the effect of metal sites and acid active sites on Mo/SBA-15, Co/SBA-15 and CoMo/SBA-15 catalysts in supercritical ethanol for the depolymerization of KL to produce phenolic monomers. Ethanol was used as a hydrogen donor solvent instead of using external hydrogen. Results showed that the bimetallic CoMo/SBA-15 catalyst exhibited significantly higher catalytic activity compared to the monometallic, Co/SBA-15, Mo/SBA-15 or bare SBA-15. The highest phenolic monomers yield of 27.04 wt% was achieved at 290 degrees C for 4 h over CoMo/SBA-15 catalyst. The inter-unit linkages such as beta-O-4 ', beta-beta and alpha-O-4 ' in lignin were considerably cleaved during the catalytic depolymerization in supercritical ethanol. Meanwhile, higher functionality of carbonyl compounds was present in the non-catalytic bio-oil, while more alkylated phenols were produced over CoMo/SBA-15 catalyst. The major phenolic monomers identified in the catalytic bio-oil were 4-ethylguaiacol (9.15 wt%), 4-methylguaiacol (6.80 wt%), and 4-propylguaiacol (2.85 wt%). These findings suggest that the metal sites and abundant acid active sites of CoMo/SBA-15 had a synergistic effect toward the degradation of different linkages of lignin and production of selective phenolic monomers in bio-oils. Kraft lignin was subjected to CoMo/SBA-15 catalyst in supercritical ethanol for high yield of alkylated-phenolic monomers production.

Automated summary

In this study, the depolymerization of Kraft lignin using Mo/SBA-15, Co/SBA-15, and CoMo/SBA-15 catalysts in supercritical ethanol was investigated. The CoMo/SBA-15 catalyst showed the highest catalytic activity and yielded the highest phenolic monomers. The metal sites and acid active sites of CoMo/SBA-15 had a synergistic effect on the degradation of lignin and production of selective phenolic monomers.