Lignin wastes: Past, present, and future

Abstract

Depletion of fossil organic raw materials has aroused the problem of switching to renewable resources. The key point in the development of technologies based on renewable sources is comprehensive utilization of renewable materials. Especially challenging is efficient involvement of wastes from processing of wood or other plant raw materials in production cycle. The main substrates in wood biomass are cellulose and partly lignin. Comprehensive utilization of plant raw materials, extension of product assortment, and minimization of wastes constitute the key problems in the development of wood processing enterprises and environmental safety. These problems may be solved via implementation of up-to-date chemical technologies and combination of works to achieve comprehensive utilization of wood. At first glance, wood resources on the Earth are huge. Forests occupy about 3.5 billion ha on the Earth surface, and wood resources amount to more than 350 billion m 3 . The annual wood increment is estimated at 5.5 billion m 3 , and the annual timber harvesting is more than 3 billion m 3 . However, taking into account high urbanization rates, reduction of forest fund, and insignificant net annual wood increment, extensive way of development of wood chemical industry seems inadmissible at present. The key product of the processing of carbohydratecontaining plant biomass is ethanol which is obtained by acid hydrolysis and is now actively offered as a promising substitute for traditional fuel. Wood conversion into ethanol, fodder yeast, and furfural in the presence of mineral acids (acid hydrolysis) is accompanied by formation of so-called “technical lignins” whose amount reaches many millions of tons per annum. Technical lignin is a large-scale waste product of microbiological industry and is a burdensome and environmentally harmful substance.