With typical carbon contents ranging from 42-54 %, biomass is a promising renewable carbon source. However, new sustainable industrial processes for conversion of biomass are required. This project presents such processes for upgrading of glycolaldehyde (GAD), which is a common by-product from degradation of larger biomass-derived compounds. Also, similar processes are investigated for some simple alcohols.
GAD is the smallest sugar, consisting of two carbons containing both an aldehyde and a hydroxyl group. Several studies on conversion of GAD into useful products have been reported, suggesting GAD to be a potential platform molecule. Still, new and sustainable protocols for the required conversion are needed.
In the project, heterogeneous supported gold nanoparticle catalysts were utilized to catalyze selective oxidation of GAD to glycolic acid, which has found applications in various industries. Up to 68 % glycolic acid was obtained at high catalyst loading, limited by CO2 formation. At a catalyst loading more fitting for industrial application, 57 % glycolic acid was obtained.
As an alternative, GAD was instead oxidized to formic acid utilizing a ceria-supported ruthenium hydroxide catalyst. Formic acid is a well-known industrial platform chemical. Recently, it has been suggested that formic acid may facilitate safe transportation and storage of hydrogen, as hydrogen can efficiently be released from formic acid. Hydrogen has multiple applications, one of them being energy conversion by fuel cells.
81 and 88 % formic acid was obtained at low and increased surface catalyst areas, respectively. Degradation of formic acid was observed for the low-surface area catalyst over time, whereas the higher-surface area catalyst was found to yield high substrate stability over time.
Oxidations of GAD at high temperatures generally resulted in over-oxidation products. However, reduced conversion was observed if temperatures were decreased too much. The optimal temperature range was found to be 80-90 °C for aqueous, base-free oxidations of GAD.
In conclusion, the project has shown that GAD can be selectively converted into either glycolic acid or formic acid, depending on the catalyst applied, under mild, aqueous and base-free conditions. High product stability in the ceria-supported ruthenium hydroxide catalyzed oxidation to formic acid, together with good catalyst activity observed when reusing the catalysts, renders the developed procedure for formic acid production highly applicable for industrial use.
Illustration:
Conversions of glycolaldehyde into various biomass derived chemicals.