2.6. Hydroprocessing
The bio-oil produced through the bio-oil stabilization processing
must be further processed to renewable diesel through hydroprocessing,
which uses hydrogen to remove excess nitrogen and
oxygen from the stabilized bio-oil. The amount of hydrogen needed
in hydroprocessing is dependent on the composition of the stabilized
bio-oil. The bio-oil composition after stabilization with
near-critical liquid propane is shown in Table 2 at two different
processing temperatures.
Hydrogen demands for hydroprocessing and renewable diesel
yields are determined based on the methods of Frank et al. [34] with
details presented in the supplementary information. The bio-oil
extracted at 23 C during the bio-oil stabilization processing yields
the best results for hydrogendemandsand energy. The bio-oil yields,
hydrogen demands, and energy inputs for hydroprocessing were
assessed based on the best values found in literature as hydroprocessing
was not preformed experimentally. The hydrogen required
and corresponding energy requirement for production for the processing
of the bio-oil is assumed to be derived from natural gas.
The energy requirements for hydroprocessing primarily result
from hydrogen production. The processing energy and material
inputs are based on a life cycle assessment of corn stover bio-oil
with bio-oil recovery through fast pyrolysis [49]. Downstream processing
of the corn stover bio-oil includes hydroprocessing which
has energy and material inputs that will be roughly the same as
those for the stabilized algal bio-oil. Material and energy input
for hydroprocessing are shown in Table 1. The bio-oil and raffinate
are assumed to have similar properties.