Hydrogenolysis of Organosolv Lignin in Ethanol/Isopropanol Media without Added Transition-Metal Catalyst

Abstract

Lignin is the largest renewable source of aromatic chemical building blocks on the planet and has great potential for the production of value-added chemicals.Herein, we describe lignin hydrogenolysis/depolymerization of organosolv poplar lignin (OPL) in ethanol/iso-propanol solvent in the absence of added catalysts. Different EtOH/i-PrOH ratios as well as various reaction conditions were evaluated. OPL depolymerization was more effective in the mixed media than in ethanol or iso-propanol alone. Heating OPL at 270 °C for 4 h in 50:50 (v:v) EtOH/i-PrOH in a closed pressure vessel gave an overall oil yield of 70 wt% of which about 48% consisted of the monomers (E)-4-propenyl syringol and iso-eugenol. Notably, these catalyst-free reactions in ethanol/iso-propanol media show monomer yields comparable to those reported for lignin depolymerization using precious metal catalysts and dihydrogen, which suggests unexpectedly favorable H-donor ability of this mixed alcohol medium.

Ambient-pressure lignin valorization to high-performance polymers by intensified reductive catalytic deconstruction

“…Products with unsaturated functional groups likely are generated because RD-RCD removes them via distillation, whereas in conventional RCD, the products undergo further hydrogenation. However, note that conventional RCD can be altered to generate more unsaturated products by eliminating external H 2 or removing the catalyst altogether at the expense of reduced yields ( 24 , 35 , 36 ). Among the lignin samples, those from harsher pulping processes, such as sample KSA, produced the lowest amount of unsaturated compounds in RD-RCD (1.4% of the phenolic products), and lignins from gentle processes, such as sample BHF, had the highest proportion of unsaturated products (11.4%), which can be rationalized on the basis of acid content in the feedstocks ( 37 , 38 ).…”

Non-catalytic oxidative depolymerization of lignin in perfluorodecalin to produce phenolic monomers

“…Non-catalytic lignin depolymerization via hydrogenolysis in ethanol/isopropanol mixtures has been reported to produce monomers at high yield. 33 However, to the best of our knowledge, effective noncatalytic, reagent-free oxidation of lignin has not been previously reported in the literature. From a safety standpoint, this was achieved without the use of flammable, peroxide-generating solvents.…”

Exploiting Nature's Most Abundant Polymers: Developing New Pathways for the Conversion of Cellulose, Hemicellulose, Lignin and Chitin into Platform Molecules (and Beyond)

“…Since conventional deligninification processes that deliver cellulose significantly degrade the lignin and so potentially devaluing it, a so‐called “lignin‐first” approach to deriving useful chemicals from it has attracted attention [48m] . This can take various forms including “organosolv” fractionation and wherein organic solvents such as methanol, ethanol, butanol, acetone, formic acid, acetic acid or even ionic liquids are used [48d,h,k,l,v] . Such fractionations are often conducted in conjunction with hydrogenolytic techniques, selective precipitations and/or membrane separations, and so providing low molecular weight aromatics that are free of sulfur‐based contaminants (as encountered in materials arising from the kraft process).…”