Challenges in industrial applications of technical lignins

Abstract

The primary aim of modern biorefineries is the efficient conversion of lignocellulosic materials into valuable products. Sugars and oils can be converted into valuable chemicals, but processing of lignin is still a challenge. A vast amount of lignin is incinerated to produce process steam and energy, and only a very small part is used for the production of value-added products. Technical lignins are isolated as by-streams in lignocellulosic refineries, e.g., as kraft, soda, organosolv, and hydrolysis lignins, as well as lignosulphonates. They have a modified structure and contain impurities that are dependent on the processing method. The structure and the composition of technical lignins restrict their subsequent applications. This paper reviews limiting factors in utilization of technical lignins. Four major classes of problems are identified, and approaches to overcoming these problems are suggested.

Dissolution of kraft lignin in alkaline solutions

“…The kraft process is considered the dominant method to remove lignin during cellulose extraction and purification, with ca. 85% of the total world lignin production being obtained by this method [17]. It employs high pHs and considerable amounts of aqueous sodium hydroxide and sodium sulfide [18], resulting in a rather hydrophobic material, kraft lignin [19].…”

Lignin Nanoparticles and Their Nanocomposites

“…However, it is not possible to completely achieve the high-value applications of lignin due to some unfavorable byproducts. The diversity of lignin sources and the complexity of the structures make the research on the potential applications of lignin have certain opportunities and challenges [23,24]. Therefore, the formation of lignin-based nanomaterials will open up a different perspective for expanding the high-value applications of lignin.…”

Catalytic Liquefaction of Kraft Lignin with Solvothermal Approach

“…Yield of monomeric products was between 10-15% depending on the lignin. The recalcitrance of lignin to conventional treatments was widely investigated [17] despite numerous reports on lignin depolymerization to produce chemicals [15]. Ether C-O bonds (β-O-4 and α-O-4) present in lignin can be readily cleaved under hydrothermal treatment, while C-C condensed linkages (mainly, 4-O-5, 5-5, β-5, β-β) require harsher conditions [18].…”