Hexahydrofarnesyl as an original bio-sourced alkyl chain for the preparation of glycosides surfactants with enhanced physicochemical properties

International audienceFive new bio-based surfactants have been synthetized by coupling hexahydrofarnesol with mono and di-saccharides. Hexahydrofarnesol (3,7,11-trimethyl-dodecan-1-ol) is a by-product of the industrial production of farnesane, a sustainable aviation fuel obtained by a fermentation process from sugar feedstocks. Using hexahydrofarnesol as the lipophilic starting material allows obtaining 100% bio-based surfactants while valorizing an industrial by-product. Moreover, the C15-branched alkyl chain brings unique properties to the surfactants. This paper presents a physicochemical characterization of these new surfactants including their behaviors in water (water solubility, critical micellar concentration and surface tension) and in oil/water systems (interfacial tension against model oil and ternary phase behavior). Their hydrophilicities have been determined thanks to the PIT-slope method and compared to the ones of standard surfactants with linear alkyl chains, in order to distinguish the contributions of the sugar polar heads and of the branched hexahydrofarnesyl lipophilic chain. This novel class of surfactants combines the properties of sugar-based surfactants (low sensitivity to temperature and salinity, ability to form Winsor III microemulsion systems over a wide range of salinity), along with specificities linked to the branched alkyl chain (lower Krafft temperature, low surface tension)

Elucidating transfer hydrogenation mechanisms in non-catalytic lignin depolymerization

Lignin undergoes catalytic depolymerization in the presence of a variety of transfer hydrogenation agents, however the mechanisms for non-catalytic depolymerization of lignin via transfer hydrogenation are not well understood; this makes process optimization difficult. Herein, for the first time a mechanism for this process is proposed. For the purposes of understanding the mechanisms involved in these non-catalytic lignin depolymerization processes, this study investigates the equilibrium system of formic acid, methyl formate and carbon monoxide, as agents for the depolymerization of lignin, in the presence of either water or methanol as solvents. In the methyl formate/water (at 300 °C) system, 73 wt% oil was produced which contained a significant amount of low molecular weight alkylphenols, with less than 1 wt% char produced. In aqueous media, the results showed that methyl formate maintains an equilibrium with formic acid which is itself in equilibrium with carbon monoxide. It was found that using either formic acid or methyl formate for non-catalytic transfer hydrogenation of lignin can produce high amounts of oil, and can be described as a two-stage mechanism. After 10 min of reaction at 300 °C, around a quarter of the formic acid is consumed via hydride transfer of the formate proton, preventing the condensation of lignin fragments. At the same time, approximately three quarters of the formic acid decomposes to carbon dioxide and carbon monoxide. Once the formic acid is consumed, the carbon monoxide was identified as the precursor to a reactive reductive reagent and was able to activate the proton of the water molecule preventing further condensation of the lignin fragments. It has been previously thought that transfer hydrogenation in lignin using formic acid occurs via the production of molecular hydrogen. Here it is demonstrated that formic acid reacts directly with the lignin, without this hydrogen formation. Therefore the key parameters for efficient transfer hydrogenation of the lignin to maximize bio-oil yield appear to involve controlling the reactions between lignin and formic acid, methyl formate or carbon monoxide under aqueous conditions, thereby reducing the reagent cost and loading while maintaining efficient lignin conversion