5 Commercial Aspects of Biomass Deconstruction with Ionic Liquids
107
in the rheological properties of the slurries produced [115]. It was found that the
shear viscosity of the produced slurry increased by three orders of magnitude upon
increasing the solid loading from 3 to 50 wt%. However, interestingly, increasing the
solid loading of the biomass improved the slurry’s shear thinning behavior, thereby
significantly reducing its complex viscosity to values similar to low solid loading.
The authors saw in this behavior an opportunity to design a high solid-loading reactor
that induced high shear stress to overcome the poor mixing limitation. Wu et al. also
investigated the role of solid loading on corn stover pretreatment efficiency using
[C 2 C 1 im][Ace] aiming to find the minimum amount of IL required for an efficient
pretreatment [116]. High glucose yields of ~80% were obtained at a wide range of
solid loading (4.8–33 wt%), while at 50 wt% solid loading the glucose yield dropped
to ~60%.
The decrease in glucose yield was attributed to a combined effect of lower lignin
extraction efficiency and less disruption of the cellulose hydrogen bonds as less
IL is present (mole ratio of [C 2 C 1 im][Ace] to glucose in cellulose). In ionoSolv
processing, doubling the biomass loading from 10 to 20 wt% for pretreatment of M.
giganteus was effective with no negative impact on process performance [108]. The
combined effect of doubling biomass loading along with shortening the pretreatment
time resulted in reducing the reactor volume by a factor of 64 which translates to a
90–95% reduction in reactor cost. A study on the impact of high solid loading on
ionoSolv pretreatment efficiency is underway and will be published shortly.
5.5.3 Ionic Liquid Recovery and Recycle
High IL recovery and recycle rates are crucial for the economic success of the process
as the amount of the IL make-up is one of the major contributors to the process
operating expenditures (OPEX) [100]. The IL cost dictates the economic significance
of the IL recycle rate and recovery; the higher the IL cost the narrower the tolerance
and vice versa. Even in the case of using a low-cost IL, an IL recovery of >95% should
be achieved for the solvent cost not to become limiting [22]. The technoeconomic
model of the IL-dissolution process also highlighted the significant impact of the IL
recovery on the process of capital expenditures (CAPEX). Low IL recovery reduces
the capacity and the cost of the IL regeneration section. However, in the process
configuration studied, because the non-recovered IL ends up flowing to the boiler,
a larger and more expensive boiler will be needed to dispose of the IL by burning.
Klein-Marcuschamer et al. showed that reducing the IL recovery from >99 to 94% at
10 wt% biomass loading decreases the CAPEX of the IL regeneration process from
$96 to $93 M while at the same time tripling the boiler costs from ~$20 to ~$60 M
[100].
Despite the technical and economic significance of IL recycle and recovery, few
pretreatment studies have investigated this aspect of the process. Even the few studies
that exist are based on IL-dissolution processes with low biomass loading (5 wt%
or less) [117, 118]. Therefore, it was important to evaluate the ionoSolv process
107
in the rheological properties of the slurries produced [115]. It was found that the
shear viscosity of the produced slurry increased by three orders of magnitude upon
increasing the solid loading from 3 to 50 wt%. However, interestingly, increasing the
solid loading of the biomass improved the slurry’s shear thinning behavior, thereby
significantly reducing its complex viscosity to values similar to low solid loading.
The authors saw in this behavior an opportunity to design a high solid-loading reactor
that induced high shear stress to overcome the poor mixing limitation. Wu et al. also
investigated the role of solid loading on corn stover pretreatment efficiency using
[C 2 C 1 im][Ace] aiming to find the minimum amount of IL required for an efficient
pretreatment [116]. High glucose yields of ~80% were obtained at a wide range of
solid loading (4.8–33 wt%), while at 50 wt% solid loading the glucose yield dropped
to ~60%.
The decrease in glucose yield was attributed to a combined effect of lower lignin
extraction efficiency and less disruption of the cellulose hydrogen bonds as less
IL is present (mole ratio of [C 2 C 1 im][Ace] to glucose in cellulose). In ionoSolv
processing, doubling the biomass loading from 10 to 20 wt% for pretreatment of M.
giganteus was effective with no negative impact on process performance [108]. The
combined effect of doubling biomass loading along with shortening the pretreatment
time resulted in reducing the reactor volume by a factor of 64 which translates to a
90–95% reduction in reactor cost. A study on the impact of high solid loading on
ionoSolv pretreatment efficiency is underway and will be published shortly.
5.5.3 Ionic Liquid Recovery and Recycle
High IL recovery and recycle rates are crucial for the economic success of the process
as the amount of the IL make-up is one of the major contributors to the process
operating expenditures (OPEX) [100]. The IL cost dictates the economic significance
of the IL recycle rate and recovery; the higher the IL cost the narrower the tolerance
and vice versa. Even in the case of using a low-cost IL, an IL recovery of >95% should
be achieved for the solvent cost not to become limiting [22]. The technoeconomic
model of the IL-dissolution process also highlighted the significant impact of the IL
recovery on the process of capital expenditures (CAPEX). Low IL recovery reduces
the capacity and the cost of the IL regeneration section. However, in the process
configuration studied, because the non-recovered IL ends up flowing to the boiler,
a larger and more expensive boiler will be needed to dispose of the IL by burning.
Klein-Marcuschamer et al. showed that reducing the IL recovery from >99 to 94% at
10 wt% biomass loading decreases the CAPEX of the IL regeneration process from
$96 to $93 M while at the same time tripling the boiler costs from ~$20 to ~$60 M
[100].
Despite the technical and economic significance of IL recycle and recovery, few
pretreatment studies have investigated this aspect of the process. Even the few studies
that exist are based on IL-dissolution processes with low biomass loading (5 wt%
or less) [117, 118]. Therefore, it was important to evaluate the ionoSolv process