A novel environmentally friendly process for depolymerization of hydrolysis lignin using Kraft cooking liquor: chemicals recoverable by the Kraft recovery cycle

Abstract

Hydrolysis lignin (HL) refers to a lignin‐rich residue obtained after the enzymatic hydrolysis of biomass. It is recalcitrant, heterogeneous, insoluble in most common solvents, and less reactive than other lignins. To enhance the reactivity of HL, a novel environmentally friendly depolymerization approach was demonstrated to produce depolymerized hydrolysis lignin (DHL) using Kraft cooking liquor, white liquor (WL) – recoverable by the Kraft recovery cycle. The effects of various process parameters such as reaction time, WL/HL ratio, and reaction temperature on lignin depolymerization were investigated using a 2 L Parr reactor under N2. The DHLs obtained were then characterized by Gel permeation chromatography (GPC)‐Ultraviolet Detector (GPC‐UV), 31P Nuclear Magnetic Resonance (NMR) spectroscopy, and ultraviolet visible (UV–visible) spectroscopy, while the filtrates were characterized by high‐performance liquid chromatography (HPLC) for saccharinic acids. The DHL yield reached 45–70% from the treatments at 150–190 °C for 1 h at a WL/HL mass ratio of 1:4 ~ 2:1. The weight‐average molecular weight (Mw) value of the DHL obtained at 190 °C after treatment for 1 h at a WL/HL ratio of 2:1 (w/w) was 2600 Da. Moreover, a significant increase in non‐condensed phenolic hydroxyl and carboxylic acid group content was observed with decreasing Mw. Compared with various existing lignin modification approaches, the approach reported here is less expensive and more environmentally friendly if integrated into Kraft pulp mill operations with the residual WL from the lignin depolymerization process being recycled to the mill chemical recovery cycle. Process scale‐up was also demonstrated using a 20 L circulating reactor. In this case, the Mw of the DHL produced after treatment at 170 °C for 2 h was 2400 Da. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Lignin valorization beyond energy use: has lignin's time finally come?

“…To address the challenges in lignin valorization for chemicals and materials as mentioned previously, we have developed an engineering approach to lignin valorization where lignin (KL or HL or OL) is firstly de-polymerized into de-polymerized lignin (DL) at a high yield (70-90%) and with a tunable M w of 1000-3000 ( Fig. 1(A)), 17,18 followed by utilizing the DL as a mixture (no separation needed) to substitute petroleum-based phenol, polyols, or bisphenol A (BPA) at a high substitution ratio of 50-100% for the synthesis of bio-based materials (Fig. 1(B)), such as bio-phenolic resins, [19][20][21] bio-polyurethane foams, 22 or lignin-based epoxy resins.…”

Revealing the Structural Influence on Lignin Phenolation and Its Nanoparticle Fabrication with Tunable Sizes

“…Lignin modifications, including methylation, demethylation, , hydrolytic depolymerization, , and phenolation, , are extensively applied in lignin research studies. As one of the most efficient ways to improve the reactivity of lignin, phenolation efficiently increases lignin’s phenolic hydroxyl group (Ph-OH) contents and active sites, which facilitates the utilization of technical lignins. , Lignin phenolation under acidic conditions is the most commonly used method. − Under strongly acidic conditions, phenols could be grafted on lignin by the electrophilic substitution between phenol and the α or γ-carbocation at a low pH value after dehydration, and then because of the cleavage of β–O–4, Cα–Cβ, and Cβ–Cγ bonds, new reactive sites are generated by releasing formaldehyde (Figure ).…”

“…4,14 Compared to proto-lignin or native lignin, KL retains fewer reactive sites and chemical modifications are usually applied to improve its reactivity and applications. 15−17 Lignin modifications, including methylation, 18 demethylation, 19,20 hydrolytic depolymerization, 21,22 and phenolation, 23,24 are extensively applied in lignin research studies. As one of the most efficient ways to improve the reactivity of lignin, phenolation efficiently increases lignin's phenolic hydroxyl group (Ph-OH) contents and active sites, which facilitates the utilization of technical lignins.…”

Lignocellulosic Biomass in Nanopesticides: A Path toward Sustainable Agriculture

“…The presence of ester groups adds reactivity to the lignin molecule, allowing these groups to participate in specific chemical reactions. This reactivity makes esterified lignin valuable for various applications, such as adhesive production and polymer modification. − …”