Fernández-Rodríguez J., Robles E., Gordobil O., González-Alriols M., Labidi J., 2016, Lignin Valorisation from Side-Streams Produced during Agriculture Waste Pulping and TCF Bleaching, Chemical Engineering Transactions, 52, 187-192.
The lignocellulosic raw materials used for cellulose production contain other interesting components such lignin. In this work, an approach for the valorisation of side-streams from cellulose extraction and purification processes was carried out. The working procedure began with a sulfur-free pulping process for the separation of lignin. It consisted in an organosolv process using ethanol-water (70:30 v/v) as white liquor during 90 min at 180 ºC and a solid to liquid ratio of 1:15. After the separation of the solid fraction from the black liquor, two total chlorine free bleaching stages were effectuated to obtain high purity cellulose for further nanocellulose production. The bleaching stages consisted in a double oxygen treatment with sodium hydroxide (1.5 % by weight). Finally, lignin from the black liquor as well as from the spent bleaching liquors was isolated by selective precipitation in order to be valorised as a source of phenolic compounds. The comparison between the obtained lignins from the different stages in term of extraction yield and physico-chemical properties was carried. Higher yields in lignin extraction were achieved from agave bagasse than from leaves (around 90 % for bagasse and more than 70 % for leaves). As it was expected, the lignin extraction yields were reduced in each stage. The purity of the lignins referred to the acid insoluble and soluble lignin, was also lower after the bleaching stages, but a level of purity higher than 75 % remained in every sample. The molecular weight distribution of all the samples and the functional chemical groups were evaluated by means of gel permeation chromatography and Fourier transform infrared spectroscopy, demonstrating the potential of the valorisation of lignin as a part of an integrated biorefinery process.
