Exploring chemical reactions to enhance thermal and dispersion stability of kraft and organosolv lignin.

Lignin has been overlooked and used as a waste for long due to its complex and partially hydrophobic structure. Many efforts have been carried out to overcome these deficiencies and apply it as a high-value product, which are insufficient to reach the full potential of lignin in various advanced applications, since they require with procedures for the obtaining of more specific and fine-tuned chemical structures. This work focuses on the obtaining of differently structured hydrophilic lignins derived both from Kraft and organosolv isolation processes. The chemical structures of the different lignin types were studied, and the effect of the structural differences in the modification processes and their subsequent properties analyzed, valorizing their potential application for diverse purposes. The carboxymethylation and sulfomethylation reactions were carried out with the aim of enhancing the polarity of the lignin samples, while the methylation reaction aimed to obtain lignins with higher stability. The physicochemical analyses of the samples, carried out by FTIR, GPC, 31P NMR, 13C NMR, and HSQC NMR, verified the effectiveness of the chemical reactions and conditions selected, obtaining lignins with lower hydroxyl content, due to their substitution and insertion of carboxymetyl, sulfomethyl and methyl groups, therefore obtaining more condensed, aromatic and oxygenated aromatic carbon structures. While the methylation reaction was the most efficient in substituting the OH groups, due to its non-selectivity, OL showed higher modification yields than KL. In terms of the thermal and morphological properties, analyzed by DLS and TGA respectively, it was observed that the modified samples showed lower Z potential values, along with higher conductivity, being the sulfomethylated organosolv lignin the one showing the best results, which was also the one with the smallest particle size and polydispersity index. Finally, all the modified samples showed higher T50% values, suggesting a better stability towards degradation.

Valorisation of crude glycerol in the production of liquefied lignin bio-polyols for polyurethane formulations.

Bio-polyols, produced by liquefying lignin with polyhydric alcohols, offer a promising alternative to conventional polyols for polyurethane production. To enhance the sustainability on the production of these bio-polyols, this study proposes the use of crude glycerol and microwave-assisted liquefaction as substitutes for conventional methods and commercial glycerol. This approach reduces the energy requirements of the reaction while also adding value to this by-product. The synthesis of bio-polyols with suitable properties to produce elastic and rigid polyurethane was carried out using previously optimised reaction conditions. Organosolv lignins obtained from Eucalyptus globulus and Pinus radiata were employed, using polyethylene glycol and crude glycerol as solvents and sulphuric acid as a catalyst. Several parameters of the bio-polyols were analysed, including hydroxyl number (IOH), acid number (An), and functionality (f), suggesting that the bio-polyols were suitable for polyurethane synthesis. Bio-polyols formulated to produce rigid polyurethanes exhibited IOH values of 554 and 383 (mg KOH/g), An values of 1.91 and 4.21 (mg KOH/g), and functionalities of 4.16 and 3.14 for Eucalyptus globulus and Pinus radiata lignin. In the case of bio-polyols for elastic polyurethanes, the values were 228 and 173 (mg KOH/g) (IOH), 20.94 and 25.09 (mg KOH/g) (An), and functionalities of 3.51 and 2.08.

Multiproduct biorefinery based on almond shells: Impact of the delignification stage on the manufacture of valuable products.

In this work, an integral valorisation of almond shells through a biorefinery approach was studied. The three main components of almond shells were extracted, isolated and characterised. The autohydrolysis process permitted the extraction of the hemicellulosic fraction obtaining a liquor rich in xylooligosaccharides (22.12 g/L). Then, two different delignification processes, alkaline and organosolv treatments, were proposed to obtain a very high purity lignin (≈90%) which could be further valorised for a wide variety of applications. The valorisation of the high cellulosic content of the delignified solids was carried out using two different methods. On the one hand, producing cellulose nanocrystals and on the other hand obtaining glucose by an enzymatic hydrolysis as well as a spent solid mainly composed by lignin (≈78 wt%). Thus, the proposed biorefinery approach could contribute to a circular economy as all the main components of the almond shells could be revalorised by environmentally friendly procedures.

Multistage treatment of almonds waste biomass: Characterization and assessment of the potential applications of raw material and products.

Almond shells are waste biomass generated in agro-industrial activities, which represent a resource that can be further valorized upon treatment. The purpose of this work was to assess new value-added products obtained through a novel multi-stage delignification process of almond shells. A comprehensive chemical characterization of the raw materials and products involved in each stage of the process was carried out. Moreover, an extensive mass balance was developed, providing a full understanding of the extraction process. The pulps produced did not display a significant cellulose loss and hence they could be exploited as cellulose-rich materials. On the other hand, the obtained lignins presented high purity values (≈90%) and a high reactivity, and their structures became more condensed and homogeneous after each extraction cycle. These features would allow their utilization as feedstock of renewable materials such bio-sourced phenolic resins.

Effect of the photocatalytic activity of TiO2 on lignin depolymerization.

Lignin is a good candidate for photocatalytic cracking due to the presence of hydroxyl groups. The photocatalytic cracking reaction involves TiO2 as heterogeneous catalyst. In the present work lignin obtained by two different pulping methods is treated under photocatalytic conditions to be depolimerized. Different exposure times to UV radiation were carried out. The results of GS-MS revealed the degradation products of the hemicelluloses contained in the lignin samples. 1h of exposure to UV radiation shows the best yield in the obtaining of lignin degradation derived compounds; the main products obtained are syringaldehyde, pyrocatechol and raspberryketone, the concentration of syringaldehyde increases 20% and vanillin 30%.