5 Commercial Aspects of Biomass Deconstruction with Ionic Liquids
111
feed temperatures of 80 and 100 °C, respectively. In addition, a very high IL recovery
of 99.9 wt% was able to be achieved in the process, which is of key importance for
an economically viable process. Despite the encouraging results, more efforts are
still needed to improve the permeate flux, selectivity, and membrane stability.
It is important to note that in IL biomass fractionation processes, such as ionoSolv where IL and water mixtures are used, only a certain amount of water needs
to be removed during the re-concentration process. In contrast, very high dehydration levels (ideally ~100%) would be needed for an IL biomass dissolution process.
In the ionoSolv process, the amount of water that needs to be removed during IL
re-concentration is equivalent to the amount of water added to precipitate lignin
from the lignin-rich IL stream. Therefore, the first attempt to optimize the process
should focus on minimizing the amount of water needed for lignin precipitation to
consequently reduce the energy requirement for IL re-concentration. In the current
lab-scale protocol, the water used for lignin precipitation is fixed at 3 g per g of IL
solution (3 water equivalents) while preliminary data suggest that 0.5 water equivalents are sufficient to precipitate >90% of the lignin [22]. A more detailed study
on the water requirement for lignin precipitation and its impact on the pretreatment
performance in the ionoSolv process is underway.
To illustrate the energy intensity of the IL re-concentration step, Fig. 5.8 compares
the energy requirement needed for the pretreatment reactor and IL re-concentration
step using a thermal evaporation unit in the ionoSolv process (based on a preliminary
techno-economic evaluation—not published).
The energy needed to increase the temperature of the reaction mixture (20 wt%
biomass loading in 20 wt% H 2 O in [N 0 2 2 2 ][HSO 4 ]) to 150 °C and reaction time of
15 min is about 5 MJ kg
−1 of biomass. On the other hand, re-concentrating the IL
solution from 60 wt% H 2 O (after lignin precipitation, assuming 1.5 water equivalents)
to initial water concentration of 20 wt% requires 15 MJ kg
−1 of biomass. The reactor
portion can be heat-integrated from available process energy reducing the energy
0
2
4
6
8
10
12
14
16
Pretreatment reactor
IL re-concentration
Energy requirement (MJ/kg)
Heat Integration
No Heat Integration
Fig. 5.8 Comparison of the energy requirement of the pretreatment reactor and IL re-concentration
(thermal evaporation) in ionoSolv process with and without heat integration
111
feed temperatures of 80 and 100 °C, respectively. In addition, a very high IL recovery
of 99.9 wt% was able to be achieved in the process, which is of key importance for
an economically viable process. Despite the encouraging results, more efforts are
still needed to improve the permeate flux, selectivity, and membrane stability.
It is important to note that in IL biomass fractionation processes, such as ionoSolv where IL and water mixtures are used, only a certain amount of water needs
to be removed during the re-concentration process. In contrast, very high dehydration levels (ideally ~100%) would be needed for an IL biomass dissolution process.
In the ionoSolv process, the amount of water that needs to be removed during IL
re-concentration is equivalent to the amount of water added to precipitate lignin
from the lignin-rich IL stream. Therefore, the first attempt to optimize the process
should focus on minimizing the amount of water needed for lignin precipitation to
consequently reduce the energy requirement for IL re-concentration. In the current
lab-scale protocol, the water used for lignin precipitation is fixed at 3 g per g of IL
solution (3 water equivalents) while preliminary data suggest that 0.5 water equivalents are sufficient to precipitate >90% of the lignin [22]. A more detailed study
on the water requirement for lignin precipitation and its impact on the pretreatment
performance in the ionoSolv process is underway.
To illustrate the energy intensity of the IL re-concentration step, Fig. 5.8 compares
the energy requirement needed for the pretreatment reactor and IL re-concentration
step using a thermal evaporation unit in the ionoSolv process (based on a preliminary
techno-economic evaluation—not published).
The energy needed to increase the temperature of the reaction mixture (20 wt%
biomass loading in 20 wt% H 2 O in [N 0 2 2 2 ][HSO 4 ]) to 150 °C and reaction time of
15 min is about 5 MJ kg
−1 of biomass. On the other hand, re-concentrating the IL
solution from 60 wt% H 2 O (after lignin precipitation, assuming 1.5 water equivalents)
to initial water concentration of 20 wt% requires 15 MJ kg
−1 of biomass. The reactor
portion can be heat-integrated from available process energy reducing the energy
0
2
4
6
8
10
12
14
16
Pretreatment reactor
IL re-concentration
Energy requirement (MJ/kg)
Heat Integration
No Heat Integration
Fig. 5.8 Comparison of the energy requirement of the pretreatment reactor and IL re-concentration
(thermal evaporation) in ionoSolv process with and without heat integration