5 Commercial Aspects of Biomass Deconstruction with Ionic Liquids
105
This can be accomplished by conducting a techno-economic analysis, or it can be
something as simple as making a back-of-the-envelope cost estimate based on some
general considerations, such as the price of the starting materials and the level of
synthesis complexity (degree of substitution and number of synthesis steps) [104,
105]. Working out the cost estimation for a new solvent, in this case, the IL, will
highlight the hot-spots that can be altered to reduce the cost. It can also reveal whether
using this new solvent for a specific process offers an economic advantage compared
to alternative solvents [95]. For the ionoSolv process, switching from an APIL to a
PIL when the process chemistry allows and then evaluating the economic viability
of using a PIL at scale sets a good example of accelerating large-scale deployment
of an IL-based process.
5.5.2 Improving Space-Time Yield
Lowering the cost of the pretreatment reactor is important to reduce the overall
process investment cost, as it is often the largest piece of capital investment in a
cellulosic ethanol plant [106]. The pretreatment reactor volume is mainly dictated
by the pretreatment time and biomass loading where higher biomass loading and
shorter time will result in a larger reactor volume [107]. Despite this, the majority
of IL-based pretreatment studies have been conducted at low biomass loading (3–
10 wt%) and long pretreatment times (8–72 h). While the knowledge obtained from
these studies is important to develop the process chemistry, such conditions cannot
be translated to an industrially relevant scale because they are uneconomical.
For example, Tao et al. estimated the capital cost of lime pretreatment to be eight
times higher than dilute-acid pretreatment due to the significant number of reactors
required (residence time of 4 h) and the need for a lime recovery unit [106].
To improve the space-time yield of a reactor, it is important to optimize the reaction kinetics, which is usually strongly dependent on temperature. Therefore, the
ionoSolv pretreatment performance for M. giganteus feedstock [22, 108] was investigated at different temperatures and residence times for using [N 0 2 2 2 ][HSO 4 ] IL
with 20 wt% H 2 O. Enzymatic hydrolysis of cellulose to glucose changed dramatically
as the recovered cellulose pulp composition varied depending on the pretreatment
severity. Reaching the optimum glucose yield is significantly accelerated when the
pretreatment is conducted at higher temperatures (Fig. 5.6).
For example, to achieve 75% glucose yield, the pretreatment should be conducted
for 15 min at 180 °C or for 8 h at 120 °C. The ability to achieve high glucose yield
while reducing the reactor volume by a factor of 32 offers a substantial economic
advantage as it translates to an optimized reactor volume and higher throughput
processing times in an industrial-scale process. This is true even if the process will
be operated at higher temperatures as the reactor energy can be supplied through
process heat integration.
As stated earlier, the ionoSolv pretreatment mechanism is based on lignin extraction from the biomass. Therefore, optimum glucose yield in enzymatic hydrolysis
should be obtained when the biomass is highly delignified [22]. Understanding the
105
This can be accomplished by conducting a techno-economic analysis, or it can be
something as simple as making a back-of-the-envelope cost estimate based on some
general considerations, such as the price of the starting materials and the level of
synthesis complexity (degree of substitution and number of synthesis steps) [104,
105]. Working out the cost estimation for a new solvent, in this case, the IL, will
highlight the hot-spots that can be altered to reduce the cost. It can also reveal whether
using this new solvent for a specific process offers an economic advantage compared
to alternative solvents [95]. For the ionoSolv process, switching from an APIL to a
PIL when the process chemistry allows and then evaluating the economic viability
of using a PIL at scale sets a good example of accelerating large-scale deployment
of an IL-based process.
5.5.2 Improving Space-Time Yield
Lowering the cost of the pretreatment reactor is important to reduce the overall
process investment cost, as it is often the largest piece of capital investment in a
cellulosic ethanol plant [106]. The pretreatment reactor volume is mainly dictated
by the pretreatment time and biomass loading where higher biomass loading and
shorter time will result in a larger reactor volume [107]. Despite this, the majority
of IL-based pretreatment studies have been conducted at low biomass loading (3–
10 wt%) and long pretreatment times (8–72 h). While the knowledge obtained from
these studies is important to develop the process chemistry, such conditions cannot
be translated to an industrially relevant scale because they are uneconomical.
For example, Tao et al. estimated the capital cost of lime pretreatment to be eight
times higher than dilute-acid pretreatment due to the significant number of reactors
required (residence time of 4 h) and the need for a lime recovery unit [106].
To improve the space-time yield of a reactor, it is important to optimize the reaction kinetics, which is usually strongly dependent on temperature. Therefore, the
ionoSolv pretreatment performance for M. giganteus feedstock [22, 108] was investigated at different temperatures and residence times for using [N 0 2 2 2 ][HSO 4 ] IL
with 20 wt% H 2 O. Enzymatic hydrolysis of cellulose to glucose changed dramatically
as the recovered cellulose pulp composition varied depending on the pretreatment
severity. Reaching the optimum glucose yield is significantly accelerated when the
pretreatment is conducted at higher temperatures (Fig. 5.6).
For example, to achieve 75% glucose yield, the pretreatment should be conducted
for 15 min at 180 °C or for 8 h at 120 °C. The ability to achieve high glucose yield
while reducing the reactor volume by a factor of 32 offers a substantial economic
advantage as it translates to an optimized reactor volume and higher throughput
processing times in an industrial-scale process. This is true even if the process will
be operated at higher temperatures as the reactor energy can be supplied through
process heat integration.
As stated earlier, the ionoSolv pretreatment mechanism is based on lignin extraction from the biomass. Therefore, optimum glucose yield in enzymatic hydrolysis
should be obtained when the biomass is highly delignified [22]. Understanding the