The anthropologic impact on climate has reached a critical level given that society relies on non-renewable fossil resources for energy. Thus, to alleviate this, lignins can play a key role in the transition from petroleum-based chemistry towards a more sustainable and green approach. The commercially available lignins are to a large extent technical lignins, which are obtained from the soda, Kraft or sulfite process, and to a lesser extent, lignins from biorefineries (i.e., organosolv and hydrolysis lignin). However, solely the incorporation of lignins at the application level is insufficient to improve sustainability and increase the greenness of processes. In this case, the path from lignin biomass to the final product should also be considered. Therefore, in this review, initially we present an adaptation of the CHEM21 metrics toolkit to assess the greenness of valorization strategies based on strategically chosen criteria. Subsequently, we present a detailed evaluation of different solvents, demonstrating the greenness of a wide variety of solvents, which will be beneficial to readers. In addition, it can be used as an instrument to design green ionic liquids that can be applied during the valorization of lignins. Furthermore, green lignin modification and depolymerization strategies (to increase the solubility, reactivity and processability and improve the structural uniformity and alter functionalities) are evaluated based on green chemistry principles considering the adapted CHEM21 metrics toolkit. Finally, the methods for processing lignins (i.e., blending and polymer synthesis) are assessed to determine if they can be considered sustainable approaches.

ZSM-22 zeolites with different Si/Al ratios (38, 50, 80) were prepared via a hydrothermal synthesis method, investigated for the catalytic dehydration of 1,3-butanediol (1,3-BDO) to butadiene (BD) at 300 °C. The catalytic performance of the synthesized materials was related to their properties and compared to a commercial ZSM-22 zeolite (Si/Al = 30). ZSM-22 (50) exhibited a quick decline in conversion, a lower BD selectivity, and higher propylene selectivity compared to the other materials, which could be attributed to the presence of strong Lewis acid sites and silanol nests. The Lewis sites favor the cracking of the intermediate 3-buten-1-ol (3B1OL) into propylene, while the silanol nests interact with the free hydroxyl group of 3B1OL, potentially inhibiting further dehydration towards BD. The highest initial BD yield of 74% was observed over ZSM-22 (80), while the highest initial BD productivity of 2.7 g_BD·g⁻¹_cata·h⁻¹ was achieved over ZSM-22 (38). After 22 h time on stream (TOS), c-ZSM-22 and ZSM-22 (38) outperformed previously reported catalysts from the literature, with productivities amounting to 1.3 g_BD·g⁻¹_cata·h⁻¹ and 1.2 g_BD·g⁻¹_cata·h⁻¹, respectively, at a site time of 6.6 mol_H+·s·mol⁻¹_1,3-BDO.