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Review
. 2020 Dec 23;22(1):63.
doi: 10.3390/ijms22010063.

Lignin for Bioeconomy: The Present and Future Role of Technical Lignin

Adam Ekielski  1 , Pawan Kumar Mishra  2
Affiliations
Review

Lignin for Bioeconomy: The Present and Future Role of Technical Lignin

Adam Ekielski et al. Int J Mol Sci. .

Abstract

Lignin, the term commonly used in literature, represents a group of heterogeneous aromatic compounds of plant origin. Protolignin or lignin in the cell wall is entirely different from the commercially available technical lignin due to changes during the delignification process. In this paper, we assess the status of lignin valorization in terms of commercial products. We start with existing knowledge of the lignin/protolignin structure in its native form and move to the technical lignin from various sources. Special attention is given to the patents and lignin-based commercial products. We observed that the technical lignin-based commercial products utilize coarse properties of the technical lignin in marketed formulations. Additionally, the general principles of polymers chemistry and self-assembly are difficult to apply in lignin-based nanotechnology, and lignin-centric investigations must be carried out. The alternate upcoming approach is to develop lignin-centric or lignin first bio-refineries for high-value applications; however, that brings its own technological challenges. The assessment of the gap between lab-scale applications and lignin-based commercial products delineates the challenges lignin nanoparticles-based technologies must meet to be a commercially viable alternative.

Keywords: bioeconomy; lignin; lignin nanoparticles; self-assembly; technical lignin.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Number of patents registered in different agencies and the number of total patents in the duration of 2000–2019 (Results were obtained from the Scopus database using the keyword “lignin”).
Figure 2
Figure 2
Common monomers of lignin.
Figure 3
Figure 3
Common linkages found in lignin [18].
Figure 4
Figure 4
Common technical lignins (* simplified and representative structures).
Figure 5
Figure 5
Cleavage of phenolic β-O-4 linkage during the kraft process [84]. Arrows represent reactions.
Figure 6
Figure 6
Representative diagram of lignin recovery by different processes. 1-evaporation and concentration: F, F1 and F2-filtrates; 2-pH adjustment to 9.5 using CO2 and aging to flocculate followed by filtration; 3-Filtrate re-slurried to pH 2 using H2SO4; 4-Filtration and washing using wash liquid (W.L.); DWL- Displacement wash liquor; 5-Oxidation using O2 followed by acidification using CO2 (pH10), coagulation and filtration; 6-Precipitate/lignin cake washing with dilute H2SO4; 7-Carbonation using CO2 and settling (pressurized); 8-Acidification using H2SO4 and brine (pressurized); 9-Washing for ash removal (water); DL-depleted liquor.Arrows represent reaction steps (Orange-Lignoboost, Grey-Lignoforce, Green-SLRP).
Figure 7
Figure 7
Representative flow diagram of general steps of Organosolv lignin production.
Figure 8
Figure 8
Reactions occurring during Lignosulfonate production [124].
Figure 9
Figure 9
Cleavage of the α and β ether linkage during the soda/alkaline process.
Figure 10
Figure 10
Acidic hydrolysis of lignocellulosic biomass [134].
See this image and copyright information in PMC

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