(428a) Production of Biofuels From Simultaneous Conversion of Hemicellulose and Cellulose in Lignocellulosic Biomass

            Replacing petroleum using biomass as
source of carbon requires the effective conversion of both the hemicellulose (C₅
sugars) and cellulose (C₆ sugars) fractions of the lignocellulosic
biomass. However, these fractions have different physical and chemical
properties making it difficult to employ a unified processing strategy for
conversion to fuels and chemicals. Accordingly, typical processing strategies
employ a pretreatment step in which the C₅ sugars are removed from
the C₆ sugars, allowing these two classes of sugars to be processed
by separate routes. The hemicellulose fraction of biomass is more reactive than
the cellulose fraction and thus, using short reaction times and low acid
concentrations it is possible to achieve high conversions of C₅ sugars
to furfural, while preserving the cellulose for other applications. Increasing
the reaction time and/or acid concentration leads to the conversion of C₆
sugars to levulinic acid, but at the expense of furfural degradation. Herein, a
process is presented that achieves the catalytic conversion of both hemicellulose
and cellulose to gamma-valerolactone (GVL), using GVL as a solvent.

A key aspect of this processing
approach is that presence of GVL minimizes subsequent degradation reactions,
which increases the furfural stability and allows for the biomass
deconstruction time to be increased. Therefore, the less reactive cellulose
fraction of biomass can be converted to levulinic acid, while retaining a high
yield of furfural thereby allowing both biomass fractions to be processed in
the same reaction step. Furthermore, using a hydrogenation catalyst, furfural
can be converted into furfuryl alcohol, which can be converted with high yields
over an acid catalyst to produce levulinic acid.

The advantages of this
unified processing approach are that (i) the hemicellulose and cellulose are processed
together, thereby eliminating the requirement of lignocelluloses fractionation,
(ii) both the hemicellulose and the cellulose are converted to the same
product, thereby eliminating the need to separate different reaction products,
(iii) the solvent used for biomass deconstruction is a product of the process, which
eliminates the need of purification steps to remove the solvent (iv) the use of
the GVL solvent leads to effective solubilization of biomass, thereby
eliminating the formation of solid humin deposits that typically lead to
reactor plugging and solids handling problems, and (v) low concentrations of
water are used in the process, thereby minimizing deactivation processes
typically observed for heterogeneous catalysts under hydrothermal conditions
(e.g., structural collapse, leaching).