(639l) Protection of Carbohydrates during Biomass Deconstruction Using Formaldehyde

Protection
of Carbohydrates during Biomass Deconstruction using Formaldehyde

Biomass-derived carbohydrates are
important platform molecules for the production of renewable fuels and
chemicals. The production of carbohydrates from lignocellulosic biomass
requires the extraction of lignin and the cleavage of ether bonds in
hemicellulose (mostly xylan) and cellulose chains while minimizing further
degradation of the resulting carbohydrates.(1) Current methods lead to
incomplete biomass depolymerization (producing only polysaccharides) and high
process costs due to mineral acid recovery and enzyme production.(2)
Lowering acid use to improve process economics requires the use of higher
temperatures and generally leads to significant sugar degradation and low
yields, which is why these strategies have generally been difficult to
implement.

Figure 1. (A) Xylose conversion to
diformylxylose and furfural during biomass pretreatment (B) Glucose conversion
to diformylglucose isomers and 5-hydroxymethylfurfural (5-HMF) during cellulose
acid depolymerization.

Recently, we have discovered that formaldehyde
(FA) could be used to stabilize lignin and facilitate the conversion of
extracted lignin to monomers at high yields (up to 97% of theoretical yield).(3) This method could also prevent xylan degradation
by producing a stable xylose-derived molecule that we refer to as
diformylxylose. In the current work, we study the stabilization of
carbohydrates by the addition of FA during integrated biomass depolymerization.
The low water content and the acidic environment in the biomass pretreatment
allow FA to react with xylose, forming diformylxylose (Figure 1-A) at yields
above 90% and minimizing xylose degradation into furfural. In comparison,
reactions without formaldehyde lead to almost full xylose degradation into
furfural with only 16% xylose recovery. Diformylxylose could be used as is or
converted back to xylose at high yields in aqueous environments. A similar
process is observed with glucose during cellulose acid depolymerization,
forming diformylglucose (DG). The presence of FA led to the formation of two DG
isomers from glucose by forming 1,3-dioxolane and
1,3-dioxane structures (Figure 1-B). As with DX, these structures stabilize
glucose after depolymerization at conditions that were previously unfavorable
due to carbohydrate degradation. Future efforts include the characterization of
protected sugars and the removal of their protective groups. 

References:

1.    J. S. Luterbacher et al., Nonenzymatic Sugar Production from Biomass Using
Biomass-Derived γ-Valerolactone. Science.
343, 277–280 (2014).

2.    L. Shuai, Y.
M. Questell-Santiago, J. S. Luterbacher, A mild biomass pretreatment using
γ-valerolactone for concentrated sugar
production. Green Chem. 18, 937–943 (2016).

3.    L. Shuai et
al., Formaldehyde stabilization facilitates lignin monomer production
during biomass depolymerization. Science. 354, 329–333 (2016).