Research ArticleAPPLIED SCIENCES AND ENGINEERING

Rapid and near-complete dissolution of wood lignin at ≤80°C by a recyclable acid hydrotrope

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Science Advances  15 Sep 2017:
Vol. 3, no. 9, e1701735
DOI: 10.1126/sciadv.1701735
  • Fig. 1 Description of the present wood fractionation experimental study and lignin solubilization mechanism.

    (A) Schematic flow diagram shows wood fractionation using p-TsOH for the production of fibers, lignocellulosic nanomaterials, sugars, and LNPs. Processes with dashed lines were not carried out in this study. (B) Schematics of carbohydrate and lignin solubilization by p-TsOH (Cp-TsOH > MHC) and precipitation (Cp-TsOH ≤ MHC).

  • Fig. 2 Effects of reaction conditions on dissolution (1 − R) of lignin (●) and carbohydrates (glucan, ⬢; xylan, ⬟; mannan, ◆).

    R is based on the component in untreated poplar wood. (A) p-TsOH concentration effects for 20 min at 80°C. (B) Temperature effects at p-TsOH concentration P = 75 wt % for 20 min. (C and D) Time effects at P = 75 wt % and 80°C (C) and at P = 80 wt % and 80°C (D).

  • Fig. 3

    Determining the p-TsOH MHC by (A) measuring the conductivities of aqueous p-TsOH solutions of different concentrations, showing discontinuity at the p-TsOH MHC of 11.5 wt % and by (B) measuring the effective size of lignin particles in diluted spent p-TsOH liquors using DLS [inset shows images of the diluted spent p-TsOH liquor with (bottom) and without (top) centrifugation].

  • Fig. 4 Demonstration of centrifugation for fractionating solubilized LNPs.

    (A) AFM images of LNPs in a diluted spent p-TsOH liquor of 10 wt % that is produced using Wiley-milled NE222 at P75T80t20. (B) AFM-measured topographical height profiles corresponding to lines 1 and 2 in (A). (C to E) AFM images of LNPs in the supernatant from the centrifuged sample in (A) at different speeds for 10 min, at 3000g (C), at 10,000g (D), and at 15,000g (E). (F) AFM-measured topographical height distributions of samples shown in (C) to (E).

  • Fig. 5 Aromatic and side-chain (δC/δH 48–140/2.5–8.0) regions in the 2D HSQC NMR spectra of the WCW and three dissolved lignin samples from poplar wood.
  • Fig. 6 Time-dependent enzymatic digestibility of fractionated NE222 WISs.

    (A) Different substrates from various fractionation conditions under constant cellulase loading of CTec3 = 20 FPU/g glucan. (B) Effects of cellulase CTec3 loading.

  • Table 1 Chemical compositions of p-TsOH fractionated poplar NE222 samples under different treatment conditions.

    The numbers in the parentheses are component yields based on components in the untreated NE222. Numbers indicate what percent of the sum of the integrals for structures Aa and Ca is accounted for by the integral for each individual structure.

    Sample labelWISsSpent liquor
    Solids yield (%)Glucan (%)Xylan (%)Mannan (%)Lignin (%)Glucose
    (g/liter)
    Xylose
    (g/liter)
    Mannose
    (g/liter)
    Acetic acid
    (g/liter)
    Furfural
    (g/liter)*
    Untreated NE22210045.714.94.623.4
    P70T50t2078.956.8 (97.9)8.8 (46.7)3.3 (56.4)20.6 (69.4)
    P70T65t2068.461.6 (92.2)6.5 (29.8)4.3 (63.9)11.8 (34.4)
    P70T50t3574.462.2 (101.1)7.4 (37.0)4.3 (68.9)19.2 (61.0)1.1 (2.2)8.9 (52.4)1.0 (20.3)1.10.05 (0.5)
    P70T65t3564.168.0 (95.3)6.6 (28.4)4.6 (64.0)13.0 (35.7)1.3 (2.5)10.1 (59.5)1.5 (29.9)1.50.08 (0.7)
    P70T80t3555.567.3 (81.7)4.9 (18.3)4.2 (50.5)6.7 (15.8)1.8 (3.6)11.6 (68.3)2.0 (38.7)1.50.19 (1.7)
    P70T80t2058.963.0 (81.1)6.5 (24.5)4.3 (53.8)8.8 (22.1)1.5 (3.0)11.0 (65.0)1.8 (35.2)1.60.13 (1.2)
    P75T65t0567.156.2 (82.4)6.5 (29.3)4.1 (60.0)15.0 (42.9)1.2 (2.4)10.1 (59.7)1.5 (29.3)1.50.07 (0.6)
    P75T65t2060.771.8 (95.4)5.8 (23.8)4.9 (63.7)10.8 (28.0)1.4 (2.7)10.8 (64.0)1.7 (32.4)1.50.10 (0.9)
    P75T65t3559.071.7 (94.5)6.0 (23.9)4.0 (51.3)8.9 (22.3)1.3 (2.6)10.3 (60.8)1.7 (32.4)1.40.10 (0.9)
    P75T65t6057.074.7 (93.1)5.0 (19.2)4.3 (52.8)7.4 (17.9)1.7 (3.2)10.7 (63.4)1.8 (34.6)1.50.14 (1.2)
    P75T80t2055.072.4 (87.1)5.2 (19.1)4.4 (52.7)6.1 (14.4)1.8 (3.6)10.9 (64.2)2.0 (39.7)1.50.19 (1.7)
    P80T80t2051.972.3 (81.9)3.7 (13.0)3.7 (41.8)4.2 (9.2)2.3 (4.6)9.9 (58.4)2.2 (43.9)1.40.33 (3.1)
    P80T80t3550.875.0 (83.4)3.6 (12.3)2.9 (31.7)4.8 (10.4)
    P80T80t6057.668.2 (85.9)3.2 (12.4)2.4 (30.0)8.3 (20.3)

    *Expressed as a percentage of total lignin content (G + S + S′ ) in each sample spectrum.

    • Table 2 Physical and chemical properties of the LNPs from dissolved lignin under three p-TsOH fractionation conditions.
      Sample
      Abbreviation
      DLS diameter
      (nm)
      Zeta potential
      (mV)
      Molecular weight
      MwMnMw/Mn
      LNP-P70T50t20349.7 ± 1.5−40.0 ± 0.2690020003.45
      LNP-P70T65t20371.7 ± 8.4−36.5 ± 0.2580021002.76
      LNP-P75T80t20467.1 ± 2.5−37.9 ± 3.6540020002.70
    • Table 3 Structural characteristics (lignin interunit linkages, PB, aromatic units, and S/G ratio) from integration of 1H–13C correlation peaks in the HSQC spectra of the WCW and three dissolved lignins from poplar wood.

      Numbers for Lignin Interunit linkages are percent of the sum of the integrals for structures Aa and Ca is accounted for by the integral for each individual structure. Numbers for PB2/6 are percentage of total lignin content (G + S + S′ ) in each sample spectrum.

      WCWP75T80t20P70T65t20P70T50t20
      Lignin interunit linkages
        β-O-4 aryl ethers (A)938787
        Resinols (C)71313
      p-Hydroxybenzoates (PB2/6)142220
      Lignin aromatic units
        G (%)363034
        S (%)647066
        S/G ratio1.82.31.9

    Supplementary Materials

    • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/9/e1701735/DC1

      fig. S1. Optical microscopy images of wood fibers produced using p-TsOH fractionation under low-severity conditions (fiber lignin content, 16%), followed by mechanical refining to 550-ml Canadian Standard Freeness.

      fig. S2. GPC-measured molecular weight distribution of LNPs from fractionation of Wiley-milled poplar NE222 using p-TsOH under three different conditions.

      fig. S3. Catalysis of carbohydrate hydrolysis and lignin degradation by p-TsOH.

      table S1. Duplicate fractionation runs under six sets of conditions to demonstrate the repeatability of p-TsOH fractionation experiments.

      table S2. Comparisons of chemical compositions of fractionated poplar NE222 WISs between the first cycle using fresh p-TsOH solution and the recycle run using spent p-TsOH acid liquor.

    • Supplementary Materials

      This PDF file includes:

      • fig. S1. Optical microscopy images of wood fibers produced using p-TsOH fractionation under low-severity conditions (fiber lignin content, 16%), followed by mechanical refining to 550-ml Canadian Standard Freeness.
      • fig. S2. GPC-measured molecular weight distribution of LNPs from fractionation of Wiley-milled poplar NE222 using p-TsOH under three different conditions.
      • fig. S3. Catalysis of carbohydrate hydrolysis and lignin degradation by p-TsOH.
      • table S1. Duplicate fractionation runs under six sets of conditions to demonstrate the repeatability of p-TsOH fractionation experiments.
      • table S2. Comparisons of chemical compositions of fractionated poplar NE222 WISs between the first cycle using fresh p-TsOH solution and the recycle run using spent p-TsOH acid liquor.

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