LIGNIN VALORIZATION PROBLEMS

The review considers two directions of lignin valorization: valorization of technical lignins, as such, without preliminary depolymerization, and valorization through monomeric compounds formed as a result of their selective destruction. The first area includes the production of lignin hydrogels, the use of lignin in medicine and pharmacology, 3D printing, as well as in the production of carbon fibers and biofuels. Lignin hydrogels are distinguished by a high sorption capacity with respect to heavy metals such as lead, iron and copper, which, depending on the content of acidic groups in lignin and the molar mass of sorbate, is ~ 25-50% of the mass of lignin, and therefore they can be used for the purification of waste waters of chemical enterprises. Lignin has high biological activity against various pathogens, including viruses, which makes research in this area very relevant, especially against the backdrop of the COVID-19 pandemic. The use of lignin in some composites for 3D printing can increase the mechanical strength of finished products. The industrial implementation of the technology for the production of carbon fibers from lignin will ensure a twofold reduction in the mass of vehicles. The second direction of lignin valorization - hydrogenolysis and selective oxidation - allows one to obtain monomeric compounds with a yield close to the theoretical one. The economic aspects of valorization are also considered. In addition, based on a comparison of the results of valorization of coniferous and deciduous lignins, a hypothesis on the structure of native lignin was proposed.