Abstract
A complete bibliometric analysis of the Scopus database was performed to identify the research trends related to lignin valorization from 2000 to 2016. The results from this analysis revealed an exponentially increasing number of publications and a high relevance of interdisciplinary collaboration. The simultaneous valorization of the three main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin) has been revealed as a key aspect and optimal pretreatment is required for the subsequent lignin valorization. Research covers the determination of the lignin structure, isolation, and characterization; depolymerization by thermal and thermochemical methods; chemical, biochemical and biological conversion of depolymerized lignin; and lignin applications. Most methods for lignin depolymerization are focused on the selective cleavage of the β-O-4 linkage. Although many depolymerization methods have been developed, depolymerization with sodium hydroxide is the dominant process at industrial scale. Oxidative conversion of lignin is the most used method for the chemical lignin upgrading. Lignin uses can be classified according to its structure into lignin-derived aromatic compounds, lignin-derived carbon materials and lignin-derived polymeric materials. There are many advances in all approaches, but lignin-derived polymeric materials appear as a promising option.
Highlights
A sustainable future requires the replacement of fossil resources for energy supply and production of chemicals
The simultaneous valorization of the three main components of lignocellulosic biomass has been revealed as a key aspect and optimal pretreatment is required for the subsequent lignin valorization
Additional tests were carried out to analyze the influence of alternative spelling variants (“valorisation” instead of “valorization”) and singular or plural forms (“lignins” instead of “lignin”), but the results demonstrated that the number of documents was not affected by these circumstances
Summary
A sustainable future requires the replacement of fossil resources for energy supply and production of chemicals. Biomass is the only natural carbon-containing resource that is available in enough quantity to replace fossil resources [1]. The expected growth of the global population and the promotion of living quality in developing countries will combine increased food and energy demands subject to restricted land availability and water supply [2]. Under these conditions, lignocellulosic biomass appears as a promising renewable raw material, since it can be obtained from marginal and degraded land and does not contribute to food supply. A significant amount of waste lignocellulosic biomass is available from the agro-industrial, pulping and paper and other sectors related to forestry
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