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Chemistry and Industry of Forest Products ›› 2020, Vol. 40 ›› Issue (6): 37-49.doi: 10.3969/j.issn.0253-2417.2020.06.006

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Synergetic Effects of Pt/ZrO2 and Lewis Acid on Reductive Depolymerization of Alkali Lignin to Phenolic Oligomers

Qian YANG1,2, Guifeng LIU1, Can JIN1, Zhenwu KONG1,*()   

  1. 1. Institute of Chemical Industry of Forest Products, CAF; National Engineering Lab. for Biomass Chemical Utilization; Key Lab. of Chemical Engineering of Forest Products, National Forestry and Grassland Administration; Key Lab. of Biomass Energy and Material, Jiangsu Province, Nanjing 210042, China
    2. Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China
  • Received:2020-03-19 Online:2020-12-28 Published:2020-12-29
  • Contact: Zhenwu KONG E-mail:kongzwlhs@163.com


A series of Pt/ZrO2 and Lewis acid co-catalytic systems, such as Pt/ZrO2-FeCl3, Pt/ZrO2-CuCl2 and Pt/ZrO2-NiCl2, were prepared for selective depolymerization of alkali lignin to generate oligomers with high content of phenolic hydroxyl groups and low content of solid residue. The effects of reaction parameters such as the component and dosage of catalysts, hydrogen pressure, reaction temperature and reaction time on the reductive depolymerization of alkali lignin were investigated. GPC, FT-IR, 31P NMR, 13C NMR and 2D-HSQC NMR were conducted to reveal the changes of structure and linkage in alkali lignin and its depolymerized products. The results showed that the synergetic catalysis of Pt/ZrO2 and Lewis acid(FeCl3, CuCl2, NiCl2) exhibited higher catalytic activity and better selectivity for phenolic compounds than Pt/ZrO2. Pt/ZrO2-FeCl3 exhibited the best catalytic activity among Pt/ZrO2-FeCl3, Pt/ZrO2-CuCl2 and Pt/ZrO2-NiCl2. Under the optimal conditions of mass ratio of Pt/ZrO2-FeCl3 to lignin 1:15, mass ratio of FeCl3 to Pt/ZrO2 0.2, reaction temperature 300 ℃, reaction time 3 h, hydrogen pressure 4 MPa, the given products with higher content of phenolic hydroxyl groups(362 mg/g) and lower content of solid residue(2.70%) were obtained, as well as, the conversion rate of lignin and the number average molecular mass(Mn) of the product were 89.0% and 998, respectively. Furthermore, the comparative structure characterization of the alkali lignin, Pt/ZrO2 catalytic depolymerization product(DL1) and Pt/ZrO2-FeCl3 catalytic depolymerization product(DL2) demonstrated that S units were more prone to be damaged during the reductive depolymerization of alkali lignin, the cleavage of methoxy groups and intramolecular β-O-4 and β-β linkages were more effective facilitated by Pt/ZrO2-FeCl3 than Pt/ZrO2.

Key words: alkali lignin, Pt/ZrO2, Lewis acids, synergetic catalysis, reductive depolymerization

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