Advancing Lignocellulosic Biomass Fractionation through Molten Salt Hydrates: Catalyst-Enhanced Pretreatment for Sustainable Biorefineries.

Developing a process that performs the lignocellulosic biomass fractionation under milder conditions simultaneously with the depolymerization and/or the upgrading of all fractions is fundamental for the economic viability of future lignin-first biorefineries. The molten salt hydrates (MSH) with homogeneous or heterogeneous catalysts are a potential alternative to biomass pretreatment that promotes cellulose's dissolution and its conversion to different platform molecules while keeping the lignin reactivity. This review investigates the fractionation of lignocellulosic biomass using MSH to produce chemicals and fuels. First, the MSH properties and applications are discussed. In particular, the use of MSH in cellulose dissolution and hydrolysis for producing high-value chemicals and fuels is presented. Then, the biomass treatment with MSH is discussed. Different strategies for preventing sugar degradation, such as biphasic media, adsorbents, and precipitation, are contrasted. The potential for valorizing isolated lignin from the pretreatment with MSH is debated. Finally, challenges and limitations in utilizing MSH for biomass valorization are discussed, and future developments are presented. Cellulose Avicel®PH-101 ZnCl 2  ⋅ 4H 2 O, ZnBr 2  ⋅ 4H 2 O, LiCl ⋅ 8H 2 O, LiBr ⋅ 4H 2 O H 2 SO 4 , (0.2 M); H 3 PW 12 O 40 (0.067 M); H 4 SiW 12 O 40 (0.05 M) T (145-175 °C); Time (30-120 min) Organic solvent (MIBK) LA (94 %) and HMF (3.4 %) Dissolution time: ZnBr 2  ⋅ 4H 2 O<> 2 O<> 2  ⋅ 4H 2 O<> 2 O; The highest conversion of pretreated cellulose and yield of glucose were obtained with ZnBr 2  ⋅ 4H 2 O (88 % and 80 %, respectively).