Catalyst Support and Solvent Effects during Lignin Depolymerization and Hydrodeoxygenation

Abstract

We studied and compared the hydrodeoxygenation (HDO) and depolymerization of aldehyde-stabilized lignin and 4-propylguaiacol (PG), a model lignin monomer. We demonstrated by liquid phase adsorption that PG HDO catalyzed by Ru/C can be achieved in isooctane but not in 1,4-dioxane due to competitive solvent binding to the active sites. Unfortunately, alkanes cannot be used as solvents for real lignin due to limited solubility. However, we show that competitive solvent binding is suppressed when switching from activated carbon to oxophilic metal oxide supports such as TiO2, yielding 32%mol of an equimolar mixture of cyclohexanes and cyclohexanols from real lignin.

Controlling lignin solubility and hydrogenolysis selectivity by acetal-mediated functionalization

“…In previous work we explored the hydrogenolysis of propionaldehyde stabilised lignin in isooctane, in which the lignin is insoluble. 43 This insolubility led to reduced monomer yields (∼70%) and shifted the monomer distribution such that predominantly hydrodeoxygenation (HDO) products were observed. Here, using our expanded lignin library, which includes highly water-soluble sodium glyoxylate stabilised lignin (≥10 wt/wt%), we can observe the true effect of converting a (solubilised) lignin in a non-polar solvent.…”

Hydrogenolysis of Lignin-Derived Aromatic Ethers over Heterogeneous Catalysts

“…Likewise, high conversion of 4-propylguaiacol HDO was observed over Ru/C in an isooctane solvent, whereas switching solvent to 1,4-dioxane lowered conversion because of the active site blocking by strongly bound 1,4-dioxane. However, such competitive binding by 1,4-dioxane could be suppressed by changing the support from activated carbon to an oxophilic oxide (e.g., TiO 2 ) . These studies highlight the importance of selecting appropriate solvents, which not only satisfy H 2 solubility requirements but have polarities matched to acid–base properties of the support.…”

“…However, such competitive binding by 1,4-dioxane could be suppressed by changing the support from activated carbon to an oxophilic oxide (e.g., TiO 2 ). 89 These studies highlight the importance of selecting appropriate solvents, which not only satisfy H 2 solubility requirements but have polarities matched to acid−base properties of the support.…”

Chemicals from Lignin: A Review of Catalytic Conversion Involving Hydrogen

“…In addition to catalysts, reaction media also play an important role in phenol production . For example, when toluene is used as solvent, some undesirable transmethylation products were formed, leading to low phenol selectivity, whereas in water the transmethylation reaction was markedly prevented, owing to the quenching effect on positive charges .…”