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Chemistry and Industry of Forest Products ›› 2023, Vol. 43 ›› Issue (1): 89-96.doi: 10.3969/j.issn.0253-2417.2023.01.011

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Modification and Characterization of Alkali Lignin by Choline-chloride/Lactic Acid Deep Eutectic Solvents Catalyzed by Sodium Carbonate

Qingye LIU1, Xianyun CHEN1, Hua DENG1, Weixing GAN1,2,*(), Siyu HUANG1, Mianwu MENG1   

  1. 1. College of Environment and Resources, Guangxi Normal University, Guilin 541006, China
    2. School of Resources, Environment and Materials, Guangxi University, Nanning 530004, China
  • Received:2021-12-07 Online:2023-02-28 Published:2023-02-28
  • Contact: Weixing GAN E-mail:gwxgxdx@126.com


The deep eutectic solvents(DES) were synthesized by choline chloride(ChCl) and lactic acid(Lac), urea(U), oxalic acid(OA) and formic acid(FA), respectively. The industrial alkali lignin(AL) was modified by these DESs. The effects of different DES systems, reaction conditions and catalysts on the extraction yield of the modified alkali lignin were studied. It was found that the extraction yield of lignin was the highest when ChCl/Lac was used. The optimal conditions of ChCl/Lac modification were obtained by single factor test. And the optimal conditions were 120 ℃, the mole ratio of Lac to ChCl(nLac/nChCl) 12 ∶ 1, mass ratio of DES to alkali lignin (mDES/mAL) 20 and reaction time 12 h, under these conditions, the extraction yield of lignin was 95.37%. When the reaction temperature was reduced to 100 ℃, the lignin extraction yield was 40.39% without catalyst. While 8% sodium carbonate was used as catalyst, the lignin extraction yield increased to 74.87%. The lignin samples were characterized by FT-IR, 13C NMR, TG and DTG. The results of FT-IR and 13C NMR showed that β-O-4 bond was broken and hydroxymethyl and methoxyl groups were introduced during modification, and the modified lignin was mainly composed of syringyl unit. From TG and DTG results, the exothermic peak of lignin moved to high temperature after sodium carbonate catalytic modification, and the thermal stability was improved.

Key words: deep eutectic solvent, choline chloride/lactic acid, alkali lignin, modification, catalysis

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