Lignin is one of the most important and widespread carbon sources on Earth. Significant amounts of lignin are delivered to the market by pulp mills and biorefineries, and there have been many efforts to develop routes for its valorization. Over the years, lignin has been used to produce biobased chemicals, materials, and advanced biofuels on the basis of its variable functionalities and physicochemical properties. Today, lignin’s applications are still limited by its heterogeneity, variability, and low reactivity. Thus, modification technologies have been developed to allow lignin to be suitable for a wider range of attractive industrial applications. The most common modifications used for this purpose include amination, methylation, demethylation, phenolation, sulfomethylation, oxyalkylation, acylation or esterification, epoxidation, phosphorylation, nitration, and sulfonation. This article reviews the chemistry involved in these lignin modification technologies, discussing their effect on the finished product while presenting some market perspectives and future outlook to utilize lignin in sustainable biorefineries.

In this review key processes for the synthesis of greener or more sustainable solvents derived from renewable sources (saccharides, lignocellulose and triglycerides) are discussed. It is shown that a series of platform chemicals such as glycerol, levulinic acid and furans can be converted into a variety of solvents through catalytic transformations that include hydrolysis, esterification, reduction and etherification reactions. It was also considered several aspects of each class of solvent regarding performance within the context of the reactions or extractions for which it is employed.

Fatty acid ethyl esters (FAEEs) were produced from waste cooking oil (WCO) using the immobilized Novozym 435 (Novozymes) lipase in a solvent-free system. WCO contained high molar mass degradation compounds that did not affect the lipase activity but remained as a minor component of the resulting FAEEs. The enzyme-catalyzed FAEE production was investigated using a central composite design. The best experimental conditions were obtained with an enzyme loading of 5 wt % and an ethanol/oil molar ratio of 6:1. Under these conditions and at the optimal enzyme temperature of 40 °C, FAEE mixtures with a total ester content of 77.2 and 89.5 wt % were produced after 10 and 24 h, respectively. Treatment of the spent biocatalyst with tert-butanol could restore the transesterification activity of the biocatalyst to its original value.

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